[meteorite-list] petrological type

From: Alan Rubin <aerubin_at_meteoritecentral.com>
Date: Sat, 12 Apr 2014 10:01:30 -0700
Message-ID: <046501cf5670$db1228c0$91367a40$_at_ucla.edu>

Since Van Schmus and Wood (1967), the group/petrologic type designation has
been entrenched (i.e., LL3.0, H4, L6), that it would be impossible to purge.
So, calling Semarkona LL T3 just won't work -- no one would adopt it as a
new convention. If we wanted to call Semarkona LL3.00 A2.8, that might be
okay, but you would have to convince people first that a two-tier system is
needed. It is probably best to exclude weathering and shock stage since we
cannot designate every property in a classification (e.g., average olivine
Fa content, cosmic-ray exposure age, oxygen-isotopic composition, chondrule
size, etc.). A problem of course is that it may be difficult to disentangle
thermal metamorphism from aqueous alteration, leaving a researcher baffled
as to what to designate a particular rock. It would be better to leave out
a classificatory parameter and to just guess and have the rock
misclassified.

Alan Rubin
Institute of Geophysics and Planetary Physics
University of California
3845 Slichter Hall
603 Charles Young Dr. E
Los Angeles, CA 90095-1567

office phone: 310-825-3202
fax: 310-206-3051
e-mail: aerubin at ucla.edu
website: http://cosmochemists.igpp.ucla.edu/Rubin.html

-----Original Message-----
From: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com] On Behalf Of Mark
Bowling
Sent: Saturday, April 12, 2014 8:13 AM
To: Meteorite List
Subject: Re: [meteorite-list] petrological type

Would the following convention work???Letter designations would be used for
each type of metamorphism.? T for Thermal and A for aqueous.? For a range of
values, a dash could be used.
?
So your example of Semarkona would end up as follows:
??? Semarkona LL T3 A2.8-2.9.

Using letter designations is already done for shock metamorphism and
weathering grade.? So when adding those, Semarkona would?become (i'm
guessing):
??? Semarkona LL T3 A2.8-2.9 S? W0

It gets to be rather cumbersome, as you say, but if it were used, one could
then quickly get an idea of the "geological" history of a particular
specimen, just from the classification.

Here is Dho 1073 as an example (and again I'm guessing on?the values):
??? Dho 1073 CV T3 A2 S2 W2-3

Capturing the order in which they occur could also be done (if you wanted to
get that much information packed into a classification scheme).? Something
earlier would be placed first.? If concurrent, they are linked with a slash.

So the prior example, thermal metamorphism would have happened first.

If aqueous alteration was first, then it would be designated as:
Dho 1073 CV A2 T3 S2 W2-3

If A & T happened together, it would be:
???? Dho 1073 CV T3/A2 S2 W2-3

But I'm not sure if that is practical - if the order is not always clear (or
if effort to make a determination is rarely given), specifying order would
be unreliable and inconsistent.? Such information, if known, would be better
communicated in the writeup.

Next, if any of these types of metamorphism?cannot or never?occur in a
particular class, you can leave out that letter.? I would think it's
safer?to not assume?it doesn't/cannot occur (simply because we don't have an
example),?and instead?use a?question mark?in place of a number.

??? e.g. Golden Mile H T4 A? S1 W1 (Congratulations Twink!).

It's pretty tedious and intimidating, but with a little practice, people
would soon be able to?understand quite a bit more about a rock just by
seeing the classification.? Plus it could always be simplified, whereby a
stone could be designated as an L3.0.? And people would pretty much
understand what that means or could imagine what it would look like.

Or for those unconcerned, they could use everything as it now is, while
scientists could adhere to the above convention in order to better
communicate with each other.

This is a interesting topic, thanks for kicking it off Francesco!
?
Have fun!
Mark?


----- Original Message -----
From: Alan Rubin <aerubin at ucla.edu>
To: 'Mark Bowling' <minador at yahoo.com>; meteorite-list at meteoritecentral.com
Cc:
Sent: Friday, April 11, 2014 10:10 PM
Subject: Re: [meteorite-list] petrological type

Several people have informally suggested a two-tier system.? It would work
something like this.? For example, on a metamorphic scale, Semarkona is type
3.00, but on an independent aqueous alteration scale it would be 2.8 or 2.9.
Similarly, CR chondrites could all be 3.0 on a metamorphic scale, but range
from 2.0 to 2.8 on an aqueous alteration scale.? This is admittedly
cumbersome, but it would be fairly useful.? However, there are some
carbonaceous chondrites that seem to have been altered and then
metamorphosed; they would be hard to deal with.? Also, if a rock is
hydrothermally altered (i.e., subjected to metamorphic heating and aqueous
alteration at the same time), that would also not be covered by such a
scheme.? Fitting complex rocks into classificatory straightjackets might
obscure more than it reveals.
Alan

Alan Rubin
Institute of Geophysics and Planetary Physics University of California
3845 Slichter Hall
603 Charles Young Dr. E
Los Angeles, CA? 90095-1567

office phone: 310-825-3202
fax: 310-206-3051
e-mail: aerubin at ucla.edu
website: http://cosmochemists.igpp.ucla.edu/Rubin.html

-----Original Message-----
From: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com] On Behalf Of Mark
Bowling
Sent: Friday, April 11, 2014 10:01 PM
To: meteorite-list at meteoritecentral.com
Subject: Re: [meteorite-list] petrological type


Are there any better alternatives that could someday replace the current
one, and do you have any references/links for them?

Thanks,
Mark

________________________________
From: Jeff Grossman <jngrossman at gmail.com>
To: meteorite-list at meteoritecentral.com
Sent: Friday, April 11, 2014 5:22 PM
Subject: Re: [meteorite-list] petrological type


Answer: you can't.? The classification scheme is lousy.

Jeff

On 4/11/2014 1:21 PM, Michael Mulgrew wrote:
> Two sequences, one for aqueous alteration and one for thermal
> metamorphism (http://www.meteoritemarket.com/PetTypeGroup.jpg).? Makes
> one wonder how we would classify a meteorite that is both thermally
> and aqueously altered...
>
>
>
Michael in so. Cal.
> IMCA 3963
>
> On Fri, Apr 11, 2014 at 10:14 AM, Francesco Moser <cojack at tiscali.it>
wrote:
>> Hello, I have a question about chondrites' petrological type number
assigned
>> after the letters (like H, L, CM or CR ...).
>> I have just read something in internet but I think I have misunderstood
>> something.
>>
>> Are the numbers from 1 to 7 in sequence or there are two different
>> sequences: 1 to 2 - 3 to 7 ??
>> 1 to 2 is for the aqueous alteration degree in carbonaceous chodrites (1
>> high degree, 2 low degree)
>> 3 to 7 is for thermal metamorphism? degree?
>>
>>
>> Thanks a lot
>>
>> Ciao
>>
>> <x>x<x>x<x>
>> Francesco
>>
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Received on Sat 12 Apr 2014 01:01:30 PM PDT