[meteorite-list] iron meteorite cooling rates and Meteorite Men

[Alan Rubin]

Magmatic iron meteorites (including the large IIIAB group) are thought to 
have formed by fractional crystallization within the cores of differentiated 
asteroids, layered by silicate mantles. Asteroidal collisions can eventually 
expose the cores (which in many or most cases have already crystallized) and 
send some of the pieces on their way to the inner solar system. Nonmagmatic 
irons (such as IAB) are more controversial.  Some think that they also 
formed in cores; others that they formed as metal melt pools at the bottoms 
of impact craters on chondritic asteroids.


Alan Rubin
Institute of Geophysics and Planetary Physics
University of California
3845 Slichter Hall
603 Charles Young Dr. E
Los Angeles, CA  90095-1567
phone: 310-825-3202
e-mail: aerubin at ucla.edu
website: http://cosmochemists.igpp.ucla.edu/Rubin.html


----- Original Message ----- 
From: "Richard Montgomery" <rickmont at earthlink.net>
To: "Alan Rubin" <aerubin at ucla.edu>; <meteorite-list at meteoritecentral.com>
Sent: Wednesday, December 15, 2010 4:47 PM
Subject: Re: [meteorite-list] iron meteorite cooling rates and Meteorite Men


> Hi List.  (ot a chemist, me, just a collector, not ametorologist, just a 
> passionate meteorite guy.
>
> This is mostly a question from Allan's post just now:  I was always under 
> the impression that  iron meteorites resulted from colliding 
> differentiated parent-bodies, and that the crystallization sequence was 
> achieved after an impact that exposed a core, molten NiFe suddenly ejected 
> into space without the shield of its former silicate mantle.  Am I way off 
> base?  Does Thompson structure develope within?
>
>
> ----- Original Message ----- 
> From: "Alan Rubin" <aerubin at ucla.edu>
> To: <meteorite-list at meteoritecentral.com>
> Sent: Wednesday, December 15, 2010 4:21 PM
> Subject: Re: [meteorite-list] iron meteorite cooling rates and Meteorite 
> Men
>
>
>> The iron meteorite cooling rates generally range from about 1 - 
>> 100ºC/Myr.
>> The reason for such slow rates is that the metal cores are buried deeply
>> within silicate mantles and heat cannot readily escape.  The coarseness 
>> of
>> the Widmanstatten pattern is a function of cooling rate -- more slowly
>> cooled irons will develop thicker kamacite lamellae.  But there are two
>> other factors that govern the coarseness of the structure -- the Ni
>> concentration and the nucleation temperature.  The lower the Ni
>> concentration in the metal, the more kamacite will develop upon cooling.
>> Metal that begins to nucleate at a higher temperature will have a longer
>> period within which kamacite can grow.
>>
>>
>>
>>
>>
>> Alan Rubin
>> Institute of Geophysics and Planetary Physics
>> University of California
>> 3845 Slichter Hall
>> 603 Charles Young Dr. E
>> Los Angeles, CA  90095-1567
>> phone: 310-825-3202
>> e-mail: aerubin at ucla.edu
>> website: http://cosmochemists.igpp.ucla.edu/Rubin.html
>>
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>