[meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis

[Mendy Ouzillou]

Thanks Jeff!

Yes, I do hope that we see more responses.
 
Mendy Ouzillou


----- Original Message -----
> From: Jeff Grossman <jngrossman at gmail.com>
> To: 'Met-List' <meteorite-list at meteoritecentral.com>
> Cc: 
> Sent: Sunday, March 16, 2014 4:39 PM
> Subject: Re: [meteorite-list] The scientific importance of subtype 3.00	meteorites and oxygen isotope analysis
> 
> Mendy and list,
> 
> My comments:
> 
> Oxygen: I would say that O isotope heterogeneity as described here is not a
> good measure of metamorphism.  Oxygen heterogeneity in these objecbulk
> samplests will be a function of sample size, as fine matrix grains
> equilibrate much more quickly than coarse ones.  If you analyze small
> aliquants of sample, most UOCs will be heterogeneous.  If, on the other
> hand, we were talking about the O isotope heterogeneity of individual
> olivine grains, akin to how we measure FeO in olivine, you might be able to
> devise a metamorphic parameter.  But so far, I'm not aware of anybody
> devising a way to use O isotopes to measure metamorphic grade.
> 
> The meaning of type 3.00: you said, "A subtype of 3.00 means that the
> material has survived unchanged by heat (radioactive decay, pressure,
> impact/shock, etc.) or aqueous alteration since its formation."  This is
> incorrect.  It means the material is unaffected by thermal metamorphism.
> Semarkona is shock stage S2, so it has been seen elevated pressures due to
> impacts on the parent body.  It also shows abundant evidence for light
> aqueous alteration. You can think of all these things as independent
> processes.  Semarkona saw little heat, but got a little shocked and a little
> bit wet.   Many CM chondrites saw little heat, but a lot of water.  I would
> call these CMs type 3.00 as well, but traditional usage has coined another
> term for really wet chondrites, namely type 2.  Oh well.   Metamorphically,
> they are type 3.00.  Some chondrites saw little shock and a lot of thermal
> metamorphism.  Anyway, all type 3.00 means is that the object saw little
> prolonged secondary heating.  The parent body may have been too small to
> differentiate, or it may have formed too late to take advantage of heat
> sources like Al-26 (and there may be other possibilities).
> 
> We are always looking for material that escaped processing on asteroids to
> learn about the origin of the solar system.  Type 3.00 chondrites are good
> for doing such studies.  CAIs are also important for early solar system
> studies, and we're fortunate that the meteorites richest in CAIs tend to be
> low petrologic types that escaped heating on asteroids as well; many
> carbonaceous chondrites are like this.
> 
> I hope this is a start at answering your questions.
> 
> Jeff
> 
> 
>>  -----Original Message-----
>>  From: meteorite-list-bounces at meteoritecentral.com [mailto:meteorite-list-
>>  bounces at meteoritecentral.com] On Behalf Of Mendy Ouzillou
>>  Sent: Sunday, March 16, 2014 12:46 PM
>>  To: Met-List
>>  Subject: [meteorite-list] The scientific importance of subtype 3.00
> meteorites
>>  and oxygen isotope analysis
>> 
>>  Well, with the LPSC going on starting this week, I sure hope we get some
>>  participation from our scientific contributors to these questions.
>> 
>>  Someone asked me to explain the scientific importance of meteoritic
> material
>>  with a 3.00 subtype. Reading through "The onset of metamorphism in
> ordinary
>>  and carbonaceous chondrites" by Grossman and Brearley 2005, I realized
> that a
>>  key tool used in the analysis of NWA 7731 and NWA 8276 was not present in
>>  the literature.
>> 
>>  So, I'll start with this first part of questions: In my discussions 
> with
> Dr. Agee, he
>>  mentioned that the heterogeneity of the oxygen isotope results is
> important
>>  because it indicates that the material has not been metamorphosed by heat
> or
>>  shock. Any heating would have caused the oxygen to begin to equilibriate.
> So, is
>>  the oxygen isotope analysis something that should be added to the list of
> factors
>>  used in evaluating low sub-types? Or is it a proxy for more complex tests?
> I am
>>  hoping that Karen Ziegler can also add some insights.
>> 
>>  The second set of questions is perhaps more complex. What is the
> scientific
>>  importance of the 3.00 subtype? I can get this one kicked off, but would
>>  appreciate a more nuanced answer than what I can provide.
>>  The subtype 3.00 represents the earliest glimpse of the properties of
> proto-
>>  planetary material in our solar system. A subtype of 3.00 means that the
>>  material has survived unchanged by heat (radioactive decay, pressure,
>>  impact/shock, etc.) or aqueous alteration since its formation. An
> implication of
>>  the unequilibrated nature of this material is that the parent body had to
> be quite
>>  small for it not to differentiate in any way.
>> 
>>  Though both scientifically important, what different types of insights do
> we gain
>>  from CAIs versus subtype 3.00 material? The answer is I am sure that they
>>  complement each other, but in what way. Which is oldest?
>> 
>>  The rarity of this type of material cannot be underestimated since between
> the
>>  only 3 known (Semarkona, NWA 7731 and NWA 8276), there is only 1,561g
>>  available for research and/or collectors. Of that total weight,
> Semarkona's 691g
>>  is almost unattainable. So, once again NWA delivers the goods!
>> 
>>  Regards,
>> 
>>  Mendy Ouzillou
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