The viscous flow behavior of lunar composition 15555, which contains about 22.5 wt % FeO, has been determined over a range of temperature from 620 ΓΈ to 700ΓΈC and from 1215 ΓΈ to 1400ΓΈC. The material was synthesized under mildly reducing conditions to simulate the Fe2+/total Fe ratio of the lunar environment. The effect of iron oxidation state on flow behavior in the high-viscosity region has been evaluated for specimens of the 15555 composition having Fe 2+/total Fe ratios of 0.94, 0.76, and 0.20. Change of the Fe :+ concentration ratio from 0.94 to 0.76 had no observable effect on the viscosity; change of the ratio from 0.76 to 0.20 resulted in a dramatic increase in viscosity by some 3 orders of magnitude at a given temperature but did not change the form of the variation of viscosity with temperature. The flow behavior is discussed and related to the structural features of the glasses.
Lunar sample 15555 is a large (9.6 kg) rock collected from the edge of the Hadley rille and has a composition corresponding to an olivinephyric mare basalt. One of the principal features of this rock is its large FeO content (β’22.5 wt %), a concentration of iron that is appreciably larger than that of any liquid whose viscous flow behavior has previously been investigated over any extensive range of viscosity. For this reason, a study of the flow characteristics of the material not only should provide information that is important for understanding its crystallization behavior but also should provide useful information about the effect of FeO content on the viscosity of silicate liquids, particularly in the highviscosity region.