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Al‐Mg systematics of CAIs, POI, and ferromagnesian chondrules from Ningqiang
Author(s) -
Hsu Weibiao,
Huss Gary R.,
Wasserburg G. J.
Publication year - 2003
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.2003.tb01044.x
Subject(s) - chondrule , chondrite , geology , melilite , geochemistry , radiogenic nuclide , olivine , plagioclase , refractory (planetary science) , parent body , meteorite , metamorphism , astrophysics , mineralogy , astrobiology , physics , paleontology , quartz , spinel , mantle (geology)
— We have made aluminum‐magnesium isotopic measurements on 4 melilite‐bearing calcium‐aluminum‐rich inclusions (CAIs), 1 plagioclase‐olivine inclusion (POI), and 2 ferromagnesian chondrules from the Ningqiang carbonaceous chondrite. All of the CAIs measured contain clear evidence for radiogenic 26 Mg* from the decay of 26 Al ( = 1.05 Ma). Although the low Al/Mg ratios of the melilites introduce large uncertainties, the inferred initial 26 Al/ 27 Al ratios for the CAIs are generally consistent with the value of 5 times 10 −5 . There is clear evidence of 26 Al* in one POI and two chondrules, but with considerable uncertainties in the value of ( 26 Al/ 27 Al) 0 . The ( 26 Al/ 27 Al) 0 ratios for the POI and the chondrules are 0.3–0.6 times 10 −5 , roughly an order of magnitude lower than the canonical value. Ningqiang shows very little evidence of metamorphism as a bulk object and the ( 26 Al/ 27 Al) 0 ratios in its refractory inclusions and chondrules are consistent with those found in other unmetamorphosed chondrites of several different classes. Our observations and those of other workers support the view that 26 Al was widely and approximately homogeneously distributed throughout the condensed matter of the solar system. The difference in ( 26 Al/ 27 Al) 0 between CAIs and less refractory materials seems reasonably interpreted in terms of a ∼2 million year delay between the formation of CAIs and the onset of formation of less refractory objects. The POI shows clear differences in 25 Mg/ 24 Mg between its constituent spinels and olivine, which confirms that they are partially reprocessed material from different sources that were rapidly quenched.