[meteorite-list] Classification question-Equilibration vs Differentation

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From: Lars Pedersen <lars.b_at_meteoritecentral.com>
Date: Thu Apr 22 10:14:08 2004
Message-ID: <3EAEE1DE.000001.01424_at_star>

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Hi Elton and list=0D
=0D
Ok I think I get it...=0D
I mix up chemical ALTERATION and thermal EQUILIBRATION right ?=0D
=0D
I think I will go back to my books, and refresh my memory.=0D
=0D
Thank you for taking time to give me the long explanation too :-)=0D
=0D
Lars =0D
=0D
-------Original Message-------=0D
=0D
From: E.L. Jones=0D
Date: 28. april 2003 23:08:57=0D
To: Lars Pedersen=0D
Cc: meteorite-list_at_meteoritecentral.com=0D
Subject: Re: [meteorite-list] Classification question-Equilibration vs
Differentation=0D
=0D
Hello All,=0D
=0D
Lars asked: Is the whole petrologic group 3 (and below) what is called=0D
unequilibrated, and from group 4 we are talking different degrees of=0D
chemical unequilibration ?=0D
=0D
So far as I am aware(<--disclaimer)The Short and Long of it.=0D
=0D
Short answer: Level 3 is the intersection point where chondrules are =0D
unaltered. Above level 3.0 is alteration due to heating and is limited =0D
to Chondrites other than Carbonaceous (E,H,L,LL,R). Levels 2 and 1 are =0D
chemical alteration (usually water) and is limited to Carbonaceous =0D
Chondrites. Level Zero (0) is used to indicate a complete absence of =0D
chondrules with no inferences as to alteration.=0D
=0D
Alteration and equilibration aren't the same processes. Alteration, as =0D
used here, is a reference to hydration and dissolution by a fluid to =0D
change the chemistry and form of the meteorite. Equilibration is the =0D
physical relaxation of boundaries on a micro level although some levels =0D
of heat and proximity may allow for minor chemistry changes.=0D
=0D
=0D
Long answer:=0D
Like the fairy tale, this is the soup bowl which was not to hot and not =0D
to cold. Equilibration is a relative process.=0D
=0D
Equilibration in this sense refers to the process of changing =0D
(metamorphosing) the original conglomeration of objects (chondrules, =0D
inclusions, etc.) within the parent body. Heating from radioactive decay =
=0D
warms up the internal areas of the parent body and slowly starts melting =
=0D
the material which has coalesced from the solar nebula.=0D
=0D
For common chondrites we must assume they started as level 3.0s. As it =0D
goes up the stages from 3-6, there are incresing degrees of change. The =0D
original boundaries between the chondrules and matrix breakdown, =0D
dissolve,etc. This results in a blend of the molecules (i.e."equalize") =0D
of various mineral pockets within the meteorite into a locally =0D
consistent and balanced mixture. When internal radioactive decay ceases =0D
or heat is lost faster than generated such as in a collision which opens =
=0D
the interior of the parent, the metamorphosing stops . To be =0D
equilibrated in this sense is to be homogenized. Note that this point is =
=0D
just short of differentiating, as in forming crystals and distinct =0D
mineral masses.=0D
=0D
If you go beyond level 6 (an undefined stage some call it level 7) you =0D
have a homogenous melt of which I don't have an approved example but =0D
look at the sort of things which happen in the acapulcoites-lodrinites =0D
etc. Additionally an impact melt is assumed to have occurred after the =0D
equilibration process and isn't a part of that process and scale even if =
=0D
it is an extreme form of melting. When the internal temperature can be =0D
held high enough, long enough--usually limited to larger bodies, it goes =
=0D
beyond "level 7" to enter the realm of Achondrites, which come from a =0D
"differentiated" body. Differentiated means the mineral molecules have =0D
migrated to zones and sorted themselves into crystals based on a myriad =0D
of factors such as density, melt temperatures, cooling rates and so on.=0D
=0D
Regards,=0D
Elton=0D
=0D
=0D
______________________________________________=0D
Meteorite-list mailing list=0D
Meteorite-list_at_meteoritecentral.com=0D
http://www.pairlist.net/mailman/listinfo/meteorite-list=0D
=2E=20
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<DIV>Hi Elton and list</DIV>
<DIV> </DIV>
<DIV>Ok I think I get it...</DIV>
<DIV>I mix up chemical ALTERATION and thermal EQUILIBRATION right ?</DIV>
<DIV> </DIV>
<DIV>I think I will go back to my books, and refresh my memory.</DIV>
<DIV> </DIV>
<DIV>Thank you for taking time to give me the long explanation too :-)</D=
IV>
<DIV> </DIV>
<DIV>Lars </DIV>
<DIV> </DIV>
<DIV id=3DIncrediOriginalMessage><I>-------Original Message-------</I></D=
IV>
<DIV> </DIV>
<DIV id=3Dreceivestrings>
<DIV dir=3Dltr style=3D"FONT-SIZE: 11pt" <i><B>From:</B></I> <A href=3D"m=
ailto:jonee_at_epix.net">E.L. Jones</A></DIV>
<DIV dir=3Dltr style=3D"FONT-SIZE: 11pt" <i><B>Date:</B></I> 28. april 20=
03 23:08:57</DIV>
<DIV dir=3Dltr style=3D"FONT-SIZE: 11pt" <i><B>To:</B></I> <A href=3D"mai=
lto:lars.b_at_pedersen.tdcadsl.dk">Lars Pedersen</A></DIV>
<DIV dir=3Dltr style=3D"FONT-SIZE: 11pt" <i><B>Cc:</B></I> <A href=3D"mai=
lto:meteorite-list_at_meteoritecentral.com">meteorite-list@meteoritecentral.=
com</A></DIV>
<DIV dir=3Dltr style=3D"FONT-SIZE: 11pt" <i><B>Subject:</B></I> Re: [mete=
orite-list] Classification question-Equilibration vs Differentation</DIV>=
</DIV>
<DIV> </DIV>
<DIV>Hello All,</DIV>
<DIV> </DIV>
<DIV>Lars asked: Is the whole petrologic group 3 (and below) what is call=
ed</DIV>
<DIV>unequilibrated, and from group 4 we are talking different degrees of=
</DIV>
<DIV>chemical unequilibration ?</DIV>
<DIV> </DIV>
<DIV>So far as I am aware(<--disclaimer)The Short and Long of it.</DIV=
>
<DIV> </DIV>
<DIV>Short answer: Level 3 is the intersection point where chondrules are=
</DIV>
<DIV>unaltered. Above level 3.0 is alteration due to heating and is limit=
ed </DIV>
<DIV>to Chondrites other than Carbonaceous (E,H,L,LL,R). Levels 2 and 1 a=
re </DIV>
<DIV>chemical alteration (usually water) and is limited to Carbonaceous <=
/DIV>
<DIV>Chondrites. Level Zero (0) is used to indicate a complete absence of=
</DIV>
<DIV>chondrules with no inferences as to alteration.</DIV>
<DIV> </DIV>
<DIV>Alteration and equilibration aren't the same processes. Alteration, =
as </DIV>
<DIV>used here, is a reference to hydration and dissolution by a fluid to=
</DIV>
<DIV>change the chemistry and form of the meteorite. Equilibration is the=
</DIV>
<DIV>physical relaxation of boundaries on a micro level although some lev=
els </DIV>
<DIV>of heat and proximity may allow for minor chemistry changes.</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>Long answer:</DIV>
<DIV>Like the fairy tale, this is the soup bowl which was not to hot and =
not </DIV>
<DIV>to cold. Equilibration is a relative process.</DIV>
<DIV> </DIV>
<DIV>Equilibration in this sense refers to the process of changing </DIV>
<DIV>(metamorphosing) the original conglomeration of objects (chondrules,=
</DIV>
<DIV>inclusions, etc.) within the parent body. Heating from radioactive d=
ecay </DIV>
<DIV>warms up the internal areas of the parent body and slowly starts mel=
ting </DIV>
<DIV>the material which has coalesced from the solar nebula.</DIV>
<DIV> </DIV>
<DIV>For common chondrites we must assume they started as level 3.0s. As =
it </DIV>
<DIV>goes up the stages from 3-6, there are incresing degrees of change. =
The </DIV>
<DIV>original boundaries between the chondrules and matrix breakdown, </D=
IV>
<DIV>dissolve,etc. This results in a blend of the molecules (i.e."equaliz=
e") </DIV>
<DIV>of various mineral pockets within the meteorite into a locally </DIV=
>
<DIV>consistent and balanced mixture. When internal radioactive decay cea=
ses </DIV>
<DIV>or heat is lost faster than generated such as in a collision which o=
pens </DIV>
<DIV>the interior of the parent, the metamorphosing stops . To be </DIV>
<DIV>equilibrated in this sense is to be homogenized. Note that this poin=
t is </DIV>
<DIV>just short of differentiating, as in forming crystals and distinct <=
/DIV>
<DIV>mineral masses.</DIV>
<DIV> </DIV>
<DIV>If you go beyond level 6 (an undefined stage some call it level 7) y=
ou </DIV>
<DIV>have a homogenous melt of which I don't have an approved example but=
</DIV>
<DIV>look at the sort of things which happen in the acapulcoites-lodrinit=
es </DIV>
<DIV>etc. Additionally an impact melt is assumed to have occurred after t=
he </DIV>
<DIV>equilibration process and isn't a part of that process and scale eve=
n if </DIV>
<DIV>it is an extreme form of melting. When the internal temperature can =
be </DIV>
<DIV>held high enough, long enough--usually limited to larger bodies, it =
goes </DIV>
<DIV>beyond "level 7" to enter the realm of Achondrites, which come from =
a </DIV>
<DIV>"differentiated" body. Differentiated means the mineral molecules ha=
ve </DIV>
<DIV>migrated to zones and sorted themselves into crystals based on a myr=
iad </DIV>
<DIV>of factors such as density, melt temperatures, cooling rates and so =
on.</DIV>
<DIV> </DIV>
<DIV>Regards,</DIV>
<DIV>Elton</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>______________________________________________</DIV>
<DIV>Meteorite-list mailing list</DIV>
<DIV><A href=3D"mailto:Meteorite-list_at_meteoritecentral.com">Meteorite-lis=
t_at_meteoritecentral.com</A></DIV>
<DIV><A href=3D"http://www.pairlist.net/mailman/listinfo/meteorite-list">=
http://www.pairlist.net/mailman/listinfo/meteorite-list</A></DIV>
<DIV>. </DIV></TD></TR>
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Received on Tue 29 Apr 2003 04:34:38 PM PDT

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