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

[Walter Branch]

Hi Jerry,

CRE = Cosmic Ray Exposure age.  An estimate of the time the rock has been in 
space.

-Walter
________________________
----- Original Message ----- 
From: "Gerald Flaherty" <grf2 at verizon.net>
To: "Walter Branch" <waltbranch at bellsouth.net>; "Meteorite List" 
<meteorite-list at meteoritecentral.com>
Sent: Saturday, November 11, 2006 2:03 PM
Subject: Re: [meteorite-list] CRE ages of Nakhlites and NWA 998


> Help! CRE age??
> Jerry Flaherty
> ----- Original Message ----- 
> From: "Walter Branch" <waltbranch at bellsouth.net>
> To: "Meteorite List" <meteorite-list at meteoritecentral.com>
> Sent: Saturday, November 11, 2006 3:15 AM
> Subject: [meteorite-list] CRE ages of Nakhlites and NWA 998
>
>
>> 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
>>
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