Rb-Sr, Sm-Nd, and Ar-Ar isotopic systematics of lherzolitic shergottite Yamato 000097

摘要

Isotopic analysis of the Martian lherzolitic shergottite Yamato 000097 yields a Rb-Sr age of 147 ± 28 Ma with an initial ~(87)Sr/~(86)Sr ratio of 0.710490 ± 0.000072, a Sm-Nd age of 152 ± 13 Ma with an initial ε~(143)Nd-value of +11.7 ± 0.2, and a ~(39)Ar-~(40)Ar age of ～260 Ma. The near concordance of these ages, in combination with the Rb-Sr and Sm-Nd initial isotopic signatures, suggests that Yamato 000097 crystallized from low Rb/Sr, light rare earth element depleted source materials ～150 Ma ago. Although the obtained ~(39)Ar-~(40)Ar age is significantly higher than the Rb-Sr and Sm-Nd ages, Yamato 000097 shows little or no evidence of trapped Martian atmospheric ~(40)Ar. The trapped ~(40)Ar concentration of Yamato 000097 is similar to that of Zagami, suggesting that both basaltic and lherzolitic shergottites may have similarly inherited excess ~(40)Ar from their magmas. The Rb-Sr and Sm-Nd ages, and initial ~(87)Sr/~(86)Sr and ε~(143)Nd-values of Yamato 000097 and Yamato 793605 lie on the same isotopic ingrowth curves, suggesting that they came from very similar mantle sources. Allan Hills 77005 was also probably derived from the same source, but Lewis Cliff 88516 appears to be from a distinct but similar source. Yamato 000097 represents the most recent known magmatism from its source, and is the youngest Martian meteorite for which concordant Rb-Sr and Sm-Nd ages have been determined.