REE adundances and Rb-Sr geochronology of Yamato-791197
The REE abundances and the Sr isotopic compositions were determined for the separated samples and the clast sample of the "lunar meteorite", Yamato-791197. Most of the features of the REE patterns are similar to those of the lunar highland samples, especially a kind of anorthosites. And the positive Ce-anomalies, shown in all REE patterns, appear characteristic of the lunar origin. The age obtained from the Rb-Sr system is 3.89±0.36 b. y. and it is considered that this age shows the time when these materials underwent an event, such as brecciation or impact melting. However, as a noticeable point, the initial ^<87>Sr/^<86>Sr is significantly low, even lower than BABI or LUNI. This result suggests that the source material of these samples might have had very low ^<87>Sr/^<86>Sr and Rb/Sr abundance ratios. The clast sample from the chip subordinate No. 109 has the distinct REE pattern and Sr-isotope ratio. Therefore, this clast can be considered to have been formed by different evolution process from the other samples, and was mingled later with them.