Al-26-Mg-26 systematics in chondrules from Kaba and Yamato 980145 CV3 carbonaceous chondrites

作者：Nagashima Kazuhide^*; Krot Alexander N; Komatsu Mutsumi

来源：Geochimica et Cosmochimica Acta, 2017, 201: 303-319.

DOI：10.1016/j.gca.2016.10.030

• Al-26(-26) Mg systematics
• Chondrules
• CV chondrites
• SIMS

We report the mineralogy, petrography, and in situ measured Al-26-Mg-26 systematics in chondrules from the least metamorphosed CV3 (Vigarano-type) chondrites, Kaba and Yamato (Y) 980145. Two Y 980145 chondrules measured show no resolvable excesses in Mg-26(Mg-26*), a decay product of a short-lived (t(1/2) similar to 0.7 Ma) radionuclide Al-26. Plagioclase in one of the chondrules is replaced by nepheline, indicative of thermal metamorphism. The lack of Mg-26* in the Y 980145 chondrules is most likely due to disturbance of their Al-26-Mg-26 systematics during the metamorphism. Although Kaba experienced extensive metasomatic alteration (< 300 degrees C), it largely avoided subsequent thermal metamorphism, and the Al-26-Mg-26 systematics of its chondrules appear to be undisturbed. All eight Kaba chondrules measured show (26) Mg*, corresponding to the initial Al-26/(27) Al ratios [(Al-26/Al-27)(0)] ranging from (2.9 +/- 1.7) X 10(-6) to (6.3 +/- 2.7) X 10(-6). If CV parent asteroid accreted rapidly after chondrule formation, the inferred (Al-26/Al-27)(0) ratios in Kaba chondrules provide an upper limit on 26 Al available in this asteroid at the time of its accretion. The estimated initial abundance of 26 Al in the CV asteroid is too low to melt it and contradicts the existence of a molten core in this body suggested from the paleomagnetic records of Allende [Carporzen et al. (2011) Magnetic evidence for a partially differentiated carbonaceous chondrite parent body. Proc. Natl. Acad. Sci. USA 108, 6386-6389] and Kaba [ Gattacceca et al. (2013) More evidence for a partially differentiated CV parent body from the meteorite Kaba. Lunar Planet. Sci. 44, abstract#1721].

• 出版日期2017-3-15