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Published September 1975 | public
Journal Article

Origin of titaniferous lunar basalts


Delineation of low pressure phase equilibria in the composition space relevant to titaniferous lunar basalts demonstrates a significant degree of control by those equilibria on the compositions of the basalts. The existence of two distinct chemical groups of basalts (high and low-K) which cannot be related one to the other by fractional crystallization at any pressure, suggests that melting is responsible for the two groups. Consideration of the pressure shift required to produce the differences between groups constrains magma segregation to have occurred in the outer 150 km of the Moon. It is difficult to relate low-Ti and high-Ti basalts to the same source region. The preferred source region of high-Ti basalts, based on phase equilibrium considerations, is a late ilmenite-rich cumulate produced from the residual liquid of the primordial differentiation of the outer portions of the Moon. This ilmenite-rich layer is sandwiched between the lunar feldspathic crust and a complementary mafic cumulate.

Additional Information

© 1975 Elsevier Ltd. Received 13 August 1974. Accepted 31 December 1974. We have benefitted from discussions with M. J. O'Hara, J. Philpotts, A. E. Ringwood, J. V. Smith, and D. R. Wones. Our microprobe is ably maintained by M. Campot. S. Adams and N. Jackson assisted in manuscript preparation. We thank R. Brett, S. Huebner, M. J. O'Hara, A. E. Ringwood, and R. J. Williams for helpful reviews. This work was supported by NASA grant NGL 22-007-247 and by the Committee on Experimental Geology and Geophysics, Harvard University.

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