The Moon is generally thought to have formed and evolved through a single or a series of catastrophic heating events, during which most of the highly volatile elements were lost. Hydrogen, being the lightest element, is believed to have been completely lost during this period. Here we make use of considerable advances in secondary ion mass spectrometry to obtain improved limits on the indigenous volatile (CO(2), H(2)O, F, S and Cl) contents of the most primitive basalts in the Moon-the lunar volcanic glasses. Although the pre-eruptive water content of the lunar volcanic glasses cannot be precisely constrained, numerical modelling of diffusive degassing of the very-low-Ti glasses provides a best estimate of 745 p.p.m. water, with a minimum of 260 p.p.m. at the 95 per cent confidence level. Our results indicate that, contrary to prevailing ideas, the bulk Moon might not be entirely depleted in highly volatile elements, including water. Thus, the presence of water must be considered in models constraining the Moon's formation and its thermal and chemical evolution.

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[1] Experimental deformation experiments have been conducted on fine-grained, twophase aggregates of olivine and orthopyroxene to investigate the role of grain and phase boundary sliding on rheology and fabric development. A suite of large-strain (g ! 1) general shear experiments conducted at T = 1200°C and P = 1.6 GPa on aggregates ranging from 65 to 0 vol % orthopyroxene, to characterize the evolution of fabric, were complemented by small-strain axial compression experiments at T = 1200°C and P = 0.3 GPa, to better constrain the rheology. Microstructural and rheological data suggest that deformation of these two-phase aggregates in the diffusion creep regime occurs via interface-reaction-controlled diffusion creep that is accompanied by extensive migration of olivine-orthopyroxene phase boundaries. The resulting rheologies suggest that olivine + orthopyroxene composites are weaker than the olivine end-member at the conditions tested. Physically, this behavior arises because long-range, i.e., grain-scale, diffusion of Si 4+ is unnecessary in these pseudobinary two-phase aggregates. We further demonstrate that interface-controlled diffusion creep leads to strong crystallographic preferred orientations (CPO) of the component minerals, which develops in the near absence of dislocation activity. The CPO formed in these anhydrous, low-stress experiments has the olivine a axis aligned perpendicular to the flow direction (''type B'' fabric) argued by some to be the unique result of deformation under conditions of high differential stress and high water fugacity. Phase boundary dynamics, thus, are argued as a significant factor in the accumulation of strain in polyphase aggregates.