[meteorite-list] Origin of chondrules

From: Jim Wooddell <jimwooddell_at_meteoritecentral.com>
Date: Wed, 13 Mar 2013 06:46:25 -0700
Message-ID: <CAH_zgwFdgNBoJwVsqXYGHnPw1vHb_W1UZK6e0XVAoA32naKs7w_at_mail.gmail.com>

Hello Alan, Jeff, Mendy,

I find this response somewhat bothersome.

I recently read a paper that little old me, not being anyone close to
being a scientist, can shoot dozens of holes through
because of the use of outdated obsolete information and now I read
this from Alan and Jeff, who I look up to and consider piers in this
field.

The fact is, people read these papers, therefore they must be true!!!
It's like the TV commericial where the girl read something on the
interenet, so it must be true because no one can put stuff on the
interent that isn't true!

So, what is going on with these papers? People are creating papers
that are supposed to be pier reviewed and here we have two piers
shooting them down in a public forum? What happen to the process of
pier review and if this particular paper is completely wrong! Who were
the piers?

I am not going to appologise for being a little critical about this
but come on guys, has it just become a paper mill? It sure beginning
to seem that way. I am completely missing the point of publishing
papers with outdated and obsolete information (when the new data is in
hand) and papers that we are reading completely wrong!

I honestly do read these papers and try to ingest as much as I can,
but here of late, it seems I am completely wasting my time reading
them and then I read your responses! Arrrrrgh.

Jim Wooddell


On Wed, Mar 13, 2013 at 3:28 AM, Jeff Grossman <jngrossman at gmail.com> wrote:
> I second what Alan wrote, at the 90% level. With my remaining finger, I'll
> add that the worst problem may be that these molten planetesimals must
> magically keep metallic and silicate melts mixed together in order to make
> chondrules, many of which have abundant metal. I think this would be
> physically difficult, to say the least.
>
> I think the ideas in this paper are philosophically quite attractive,
> joining modern research on cosmochronology with dynamical models of the
> disk. But despite this new way of thinking, the basic tenets are quite
> retro. Many people up through the 1960s hypothesized that chondrules were
> fragments of igneous rock. Then modern research on them began. Study after
> study found problems with these models, many of which Alan outlined.
> Although the new model is a twist on the old ones, it still is subject to
> the same tests... and it cannot pass most of them.
>
> Jeff
>
>
> On 3/13/2013 2:03 AM, Alan Rubin wrote:
>>
>> I'll be happy to give my opinion on the paper. I think it is completely
>> wrong. Here is my reasoning:
>> 1. Many chondrules are surrounded by secondary igneous shells, still
>> others by igneous rims. These shells and rims indicate that the chondrules
>> haev experienced more than one melting event.
>> 2. Many FeO-rich (i.e., Type-II) porphyritic olivine chondrules contain
>> relict grains of different FeO contents and different O-isotopic
>> compositions, again indicating multiple melting. This is very hard in a
>> collision model.
>> 3. One might expect molten planetesimals to have well-mixed melts. If
>> the chondrules are mainly from the larger planetesimal (the target) as one
>> would expect, the O isotopic compositions of the chondrules would probably
>> be mass-fractionated and lie on a slope-1/2 line on the standard
>> three-isotope diagram. We don't see this.
>> 4. One might also expect that as the planestimal melted and began to
>> crystallize, it would become chemically fractionated, unlike the
>> unfractionated, solar, compositions of chondrules in primitive chondrites.
>> 5. The occurrence of microchondrules in the fine-grained rims around some
>> normal-size chondrules and the apparent melting of pyroxene at the outer
>> surface of the chondrule to form the microchondrules indicates chondrule
>> melting by a mechanism capable of melting only the outer surface of the
>> chondrule. This is totally inconsistent with the formation by splashing by
>> the collision of molten planetesimals.
>> 6. There are correlations between chondrule size, the proportion of
>> different chondrule types, the proportion of those with igneous rims and
>> secondary shells that are difficult to explain by splashing but come
>> naturally to a model invoking multiple melting in dusty nebular regions.
>> 7. The non-spherical shapes of most CO chondrules indicates very rapid
>> cooling or else they would have collapsed into spheres. This might be okay
>> except for the fact that the large size of their phenocrysts require a
>> growth period thousands of times longer than the time it would take a molten
>> droplet to collapse into a sphere. This again indicates a flash heating
>> mechanism.
>> 8. The fairly rare occurrence of chondrule-CAI mixtures are difficult to
>> explain by colliding molten planetesimals, but are sinple to explain by
>> melting of a mafic dustball that had and old CAI fragment inside.
>> 9. Each chondrite group has its own distinctive narrow range of chondrule
>> sizes. In fact, about 90% of the chondrules in any group have diameters
>> within a factor of 2 of the mean size. One would expect molten
>> planetesimals to produce a similar size of chondrules range for each group.
>> Furthermore, chondrule size is correlated with lots of other chondrule
>> properties (proportions of textural types, numbers with rims and secondary
>> shells, etc.) that are hard to explain by molten planetesimals.
>> 10. And, I just don't see how we get the different chondrule textural
>> types by that model. Some chondrules lack olivine, others lack pyroxene,
>> some are coarse grained, some are fine-grained, some have a mixture of
>> different size grains, some include relict grains. This seems impossible to
>> produce by the molten planetesimal model.
>> Since I only have 10 fingers, I'll stop there.
>>
>>
>> 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: "Mendy Ouzillou" <ouzillou at yahoo.com>
>> To: "met-list" <meteorite-list at meteoritecentral.com>
>> Sent: Tuesday, March 12, 2013 7:06 PM
>> Subject: [meteorite-list] Origin of chondrules
>>
>>
>> And now for something completely different ... Meteorite talk.
>>
>>
>> I am in the process of reading through a fascinating article in latest
>> issue of "Meteoritics and Planetary Science" called "The Origin of
>> Chondrules and Chondrites: Debris from Low Velocity Impacts Between Molten
>> Planetisimals."
>>
>> This paper is very well written and readable even by a novice such as
>> myself. What I find interesting is the proposal for a (somewhat) new theory
>> that chondrules did not instantly form from clumps of heated nebular dust
>> but instead formed 1.5 to 2.5MY after the formation of CAIs. the paper
>> states that chondrules formed from splashing when two differentiated
>> planetisimals collided at a relatively slow speed of between 10 to 100m/s.
>> Without being able to review the previous papers, I have to say that to me
>> this makes a great deal of sense and appears to solve many of the
>> inconsistencies that have been raised in some of the older books that I have
>> read.
>>
>> Note: there is a typo in the paer on page 2177. Is states "A strength of
>> the splashing model is that it can explain why chondrules are mostly between
>> 1.5 and 2.5MYr younger than CAI ...". The sentence should read "older", no
>> "younger".
>>
>> Dr. Jeff Grossman, would love to hear your thoughts on this paper.
>>
>> Mendy Ouzillou
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-- 
Jim Wooddell
jimwooddell at gmail.com
928-247-2675

Received on Wed 13 Mar 2013 09:46:25 AM PDT