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

From: Mendy Ouzillou <ouzillou_at_meteoritecentral.com>
Date: Sun, 16 Mar 2014 22:09:03 -0700 (PDT)
Message-ID: <1395032943.67048.YahooMailNeo_at_web162605.mail.bf1.yahoo.com>

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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Received on Mon 17 Mar 2014 01:09:03 AM PDT