i see.
since you found the referenced paper, can you post how this apparent snafu was solved?
It wasn't a snafu, it was a discovery that is unique to minerals such as cubic diamonds formed only in the mantle. According to Zashu et al (actually Ozima was the lead author not Zashu as stated by Pitman) state that:
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[/FONT][FONT=times, times new roman, serif]Cubic diamonds from Zaire show excellent correlations between potassium content and 40Ar/36Ar ratio, and between 40Ar/36Ar and 39Ar/36Ar, which can be interpreted to yield an 'isochron' age of about 6 Gyr. Now the discovery of a correlation between chlorine content and 40Ar, together with recent mineralogical and geochemical work concerning the origin of cubic diamonds, strongly suggests that the 40Ar is an excess component which has no age significance, and that the 40Ar and its associated potassium are contained in sub-micrometre inclusions of mantle-derived fluid.[/FONT]
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More recent work reinforces what Zashu, Ozima et al discovered. Here are links to these works.[/FONT]
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http://www.researchgate.net/profile/Jan_R_Wijbrans/publication/223835881_40Ar39Ar-ages_of_phlogopite_in_mantle_xenoliths_from_South_African_kimberlites_Evidence_for_metasomatic_mantle_impregnation_during_the_Kibaran_orogenic_cycle/links/0fcfd509c21f9b403c000000.pdf[/FONT]
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https://journals.uair.arizona.edu/index.php/maps/article/download/15607/15595[/FONT]
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http://onlinelibrary.wiley.com/doi/10.1029/2010GC003073/full[/FONT]
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http://www.researchgate.net/profile/Jo_Anne_Wartho/publication/249551276_40Ar39Ar_ages_in_mantle_xenolith_phlogopites_determining_the_ages_of_multiple_lithospheric_mantle_events_and_diatreme_ascent_rates_in_southern_Africa_and_Malaita_Solomon_Islands/links/0c96053556507dd9c7000000.pdf[/FONT]
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http://www.nature.com/nature/journal/v334/n6183/abs/334607a0.html[/FONT]
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http://www.nature.com/nature/journal/v323/n6090/abs/323710a0.html[/FONT]
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http://www.sciencedirect.com/science/article/pii/0016703783900443
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my mistake about ar/ar dating.
Thank you, we all make mistakes.
