MG diffusion in anorthite - Survival of the Al-26 chronometer

Details MG diffusion in anorthite - Survival of the Al-26 chronometer MG diffusion in anorthite - Survival of the Al-26 chronometer

Mar 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997lpi....28..781l&link_type=abstract

Conference Paper, 28th Annual Lunar and Planetary Science Conference, p. 781.

Computer Science

5

Magnesium, Particle Diffusion, Anorthosite, Aluminum, Chronometers, Chondrule, Single Crystals

Scientific paper

The presence of excess Mg-26 (from the decay of short-lived Al-26) provides key constraints on the time interval between Al-26 production in the interstellar medium and the formation of early solar system objects. Insofar as Al-26/Al-27 was initially uniform throughout the solar system, the Al-26-Mg-26 system can serve as a chronometer for events in the early solar system. If Al-26/Al-27 was initially uniform throughout the solar system, the large range in (Al-26/Al-27)o indicates that CAI and chondrule formation spanned over 5 Ma. A potential complication with this interpretation, however, is postcrystallization redistribution of Mg such as might occur during thermal metamorphism on protoplanets. In this case the Al-26-Mg-26 systematics would give no time information. Excess Mg-26 can thus far only be resolved in phases with Al/Mg above about 10, such as plagioclase. No data for Mg diffusion in plagioclase exist, however, and previous estimates of Mg diffusivity have been based on data for Sr. Here we present the first measurements of Mg self diffusion in anorthite. We then use these data to calculate the conditions under which Mg will isotopically exchange with surrounding phases and thus establish bounds on the thermal conditions required to preserve or destroy the Al-26 chronometer in anorthite.

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