ABSTRACT

The high content of titanium and many refractory trace elements is a remarkable feature of many lunar basalts, and its origin is imperfectly understood. A unique titanium-rich pyroxene in the Allende meteorite shows an abundance pattern for Ti, Ba, Sr, rare earth elements, Y, Zr, Hf, and Nb paralleling that for the high-titanium lunar basalts. Its probable origin as a high-temperature condensate from the primitive solar nebula indicates that it may have been an important phase in the original accretion of the Moon. A small degree of partial melting of material containing this phase would give a magma with abundance patterns for these elements comparable to those measured in basalts collected on the Apollo 11 and 17 missions; the younger and less Ti-rich basalts of other missions can plausibly be explained by a greater degree of partial melting and dilution with other phases.