[meteorite-list] CRE ages of Nakhlites and NWA 998

[Walter Branch]

Hello Everyone,

I have been studying nakhlites in general and martian meteorite NWA 998 in 
particular.  This paper,
http://www-curator.jsc.nasa.gov/antmet/mmc/XXV_NWA998.pdf

quotes a CRE of 9.3 m.y. using 38Ar.  This paper

http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1137.pdf

quotes a CRE age of 9.4 m.y, again using 38Ar.  However, the paper further 
points out CRE ages using 3He and 21Ne are in better agreement (12.2 and 
11.7 m.y., respectively) and are in agreement with other nakhlite CRE ages. 
The authors state, "All nakhlite CRE ages based on Ar are significant (sic) 
younger than those based on He and Ne, an unexplained characteristic also 
observed among some shergotite CRE ages."

Does anyone know why this is?

-Walter Branch

________________________