[meteorite-list] Bull's-eye chondrule assumptions (& New Meteorite Atlas)

From: Gerald Flaherty <grf2_at_meteoritecentral.com>
Date: Wed May 4 08:52:44 2005
Message-ID: <04ff01c550a8$23dad940$2f01a8c0_at_Dell>

Hi Jeff and List,
Jeff you use the term bleaching, is that an oxidation process?
Jerry Flaherty
----- Original Message -----
From: "Jeff Grossman" <jgrossman_at_usgs.gov>
To: <Meteorite-list_at_meteoritecentral.com>
Sent: Wednesday, May 04, 2005 8:30 AM
Subject: Re: [meteorite-list] Bull's-eye chondrule assumptions (& New
Meteorite Atlas)


> Oh, I didn't see the other question in this thread. The "bites" out of
> "pac-man" chondrules can have one of two origins. The most popular
> explanation is that the chondrule underwent a low-velocity collision with
> another chondrule during the time in its cooling history when it was
> mostly crystallized but still warm and plastic. However, a much better
> explanation for some of these, including the ones in some of your photos I
> think, is that the chondrule originally contained a significant amount of
> Fe-Ni metal and/or FeS. This formed a round bead when the chondrule was
> cooling and migrated to the surface due to centrifugal force as the
> chondrule was spinning. At some point after the chondrule solidified, the
> metal/sulfide bead was lost. There is a picture of a chondrule that still
> has the metal bead in place in a paper I wrote 20 years back (Grossman &
> Wasson 1985, GCA 49, 925-939, The origin and history of the metal and
> sulfide components of chondrules).
>
> Whichever reason for the "crater" is correct, bleaching occurred on the
> parent asteroid, following the contours of the crater.
>
> Jeff
>
> At 03:32 AM 5/4/2005, Jeff Kuyken wrote:
>>I was just going through my emails and found this one. Well, I have just
>>received Marvin Killgore's new "A Color Atlas of Meteorites in Thin
>>Section"
>>from Mike Jensen. I highly recommend this book which has numerous
>>fantastic
>>images of MANY different meteorite types.
>>
>>One of the things I noticed was that a few of the meteorites presented
>>actually have Bull's-eye chondrules. For those of you who may have
>>purchased
>>this book, the page references I have found so far include:
>>
>>NWA 487 (L/LL3.2) P20-23
>>LEW 86018 (L3.1) P44-47
>>ALH 77176 (L3.2) P48-51 (Remnant/Damaged)
>>QUE 97008 (L3.4) 56-57
>>LEW 87284 (L3.6) P64-67
>>ALH 85033 (L4) P72-73
>>GOLD BASIN (L4) P76-79 (Remnant/Weathered)
>>MOUNT TAZERAIT (L5) P80-81
>>
>>Any thoughts?
>>
>>Jeff
>>
>>
>>----- Original Message -----
>>From: bernd.pauli_at_paulinet.de
>>To: Meteorite-list_at_meteoritecentral.com
>>Sent: Thursday, March 17, 2005 7:48 AM
>>Subject: [meteorite-list] Bull's-eye chondrule assumptions
>>
>>
>>John and Dawn wrote:
>>
>> > We seem to have several of them in our new LL3
>>
>>Christian responded and presented some stunning pictures:
>>
>> > I have many of them: ...
>>
>>Whereupon John and Dawn wrote:
>>
>> > I really liked NWA 1770
>>
>>I am in love with the perfect bull's eye in Christian's NWA 724!
>>
>> > www.austromet.com/collection/NWA_0724_5.646g.jpg
>>
>>Do I have any ideas on the formation of such chondrules?
>>
>>Only some ideas, no references, no direct links: These chondrules
>>obviously occur only in unequilibrated chondrites of types H3.x,
>>L3.x, and LL3.x (by inference probably also in some E3 chondrites),
>>up to petrologic type 4.
>>
>>Darker core material seems to be enveloped by a lighter-colored, in
>>some cases almost concentric ring of (fine-grained, dusty?) material.
>>
>>The process that gave birth to such chondrules may have been either
>>accretionary or condensational and the environment may have been
>>dusty (which would point to early solar system processes).
>>
>>Obviously only a limited number of chondrules underwent this process
>>so that the bull's-eye chondrule formation may have been a selective
>>process (time, distance from the protosun, dusty environment..I don't
>>know).
>>
>>It would be interesting and helpful if someone detected such bull's-eye
>>chondrules in one of their thin sections so that we could draw further
>>conclusions on their mineralic compositions (core material, rim or seam
>>(?) material, high-temperature, low-temperature phases, etc.).
>>
>>Esteemed list member Jeff Grossman wrote several papers on chondrule
>>formation, chondrule composition, zoned chondrules, etc. Maybe he can
>>enlighten us on these "Eyes of Taurus", the Bull, my Constellation :-)
>>
>>Best wishes,
>>
>>Bernd
>>
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Received on Wed 04 May 2005 08:50:47 AM PDT