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Author Topic:   The radiometric dating of basalts
Member (Idle past 1699 days)
Posts: 97
From: Australia
Joined: 08-02-2010

Message 8 of 10 (660126)
04-21-2012 8:03 AM
Reply to: Message 1 by Minnemooseus
08-15-2009 9:19 PM

Dating Basalt
I see the OP is pretty old, but in light of some recent activity I'd like to add my two cents worth.

Firstly Baddeleyite is a zirconium oxide found in mafic rocks. Although wiki (http://en.wikipedia.org/wiki/Baddeleyite) describes it as rare, I have had a pretty good success rate having it identified and dated in samples of terrestrial basalts and gabbros I have collected.

Secondly, and possibly more importantly, is the development of the SHRIMP (proudly Australian!). The SHRIMP (http://en.wikipedia.org/wiki/SHRIMP) can measure isotopic abundance at micrometre scale to a high degree of accuracy so thus only a small amount of material is required to get, for example, a U-Pb date. Older dating techniques required the collection of a substantial number of zircon grains which were then digested in acid to get measure their isotopic abundances. Obviously collecting enough zircon from mafic materials was often very difficult. Additionally, this technique could sometimes give spurious results if zircons with a complex crystallisation history (ie zoned zircons) were not identified and removed from the sample set. The SHRIMP is sensitive enough to date each zircon individually, so it is fantastic for rock types were zircon minerals are rare, and in some instances in can date individual zones within a single zircon crystal to give a crystallisation age for each zonation. Good times for geochronologists!

This message is a reply to:
 Message 1 by Minnemooseus, posted 08-15-2009 9:19 PM Minnemooseus has replied

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