Thanks Jeff! Yes, I do hope that we see more responses. Mendy Ouzillou
----- Original Message ----- > From: Jeff Grossman <[email protected]> > To: 'Met-List' <[email protected]> > 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: [email protected] [mailto:meteorite-list- >> [email protected]] 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 >> ______________________________________________ >> >> Visit the Archives at http://www.meteorite-list-archives.com >> Meteorite-list mailing list >> [email protected] >> http://six.pairlist.net/mailman/listinfo/meteorite-list > > > ______________________________________________ > > Visit the Archives at http://www.meteorite-list-archives.com > Meteorite-list mailing list > [email protected] > http://six.pairlist.net/mailman/listinfo/meteorite-list > ______________________________________________ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list [email protected] http://six.pairlist.net/mailman/listinfo/meteorite-list
