[meteorite-list] Chelyabinsk - slickensides or shock planes?

From: Jim Wooddell <jim.wooddell_at_meteoritecentral.com>
Date: Tue, 21 May 2013 15:17:49 -0700
Message-ID: <519BF28D.5050900_at_suddenlink.net>

Hi Bernd!

Doesn't sound like that discussion came to any conclusion. I think there
was one in 2003 too!

I think this discussion has been going on since prior to 1966, ref the
abstract link I posted.
I do see striations and typically the slickensides I am familiar with
are typically larger, not tiny parts of very small rocks. Hundreds of
pictures of it on the web.
I'd really like to see a scientific explanation for them in meteorites
as very small parts of small rocks as they are being defined. Sort of
looking around for an explanation and haven't found anything at this
time. The ones in Anne's pictures, for example, are not part of an
individual clast that could have been a bigger rock that had
slickensides and you can clearly see breccias suggesting that feature
happened after things came together. I think I also see a contiguous
border, not strings that are continuous which, to me, would indicate it
part of something bigger.
Then how to explain a weak boundary that just happens to contain
slickensides considering how these boundaries were formed in the first
place! I love it!


Jim


On 5/21/2013 2:36 PM, Bernd V. Pauli wrote:
> Hello All,
>
> We had a similar discussion many, many years ago
> (September 2001). Here's a short overview of our results:
>
> Summary:
>
> - broken surface is covered with glossy striations
> - slickensides are identified by shiny mirror like surfaces
> on an otherwise rough rock
>
> - they are the product of faulting in a rock body (as the crust
> shifts, even slightly, the roughness of the rock tends to smooth)
>
> - slickensides are formed from the movement of rocks relative to each other
> along fracture planes in fault zones
>
> - rub your finger along the grooves which make up the slickensides:
>
> * they feel rough when you move your finger in the direction opposite
> to which the adjacent rock moved to form the slickensides
>
> + they feel smooth when you rub in the same direction the adjacent rock
> moved because it sheared off any microscopic projections or rough
> edges as it moved
>
> => Not found in shatter cones!
>
> - slickensides are formed when opposite sides of rock faults
> move in different directions
>
> - extreme pressure generates frictional heat as the rock faces are forced
> past each other partially melting a thin veneer of rock at the interface
>
> (result: smoothing of rough edges and a polished looking surface)
>
> - they are not formed by explosive breakup in the earth's atmosphere
> (in such a breakup pieces would be flying apart from each other
> whereas in slickensides the opposite is happening: the rock faces
> are being forced against each other) but: see below **
>
> - possible formation scenario: an impact event in space results in
> movement of two adjacent parts of the stony meteorite relative to
> each other along a preexisting fracture plane thus creating grooves
>
> - slickensides are polished, grooved surfaces that occur along shear planes
>
> - slickensides form along internal shear planes as opposite parts
> move past one another
>
> - opposite parts rub against each other, their surfaces become smoothed,
> lineated, and grooved
>
> - slickensides are formed when two planar sides grind past each other
>
> - slickensides can be created at the moment of breakup (not by the explosive
> part of this breakup but rather when two parts of the meteorite grind past
> each other along a pre- existing fracture ? so-called shear rupturing) **
>
> and here are some of the listees that participated in the discussion:
>
> Charlie Devine (started the discussion), Eric Olson, Robert Verish,
> ... to name a few.
>
> Cheers,
>
> Bernd
>
>
>
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Received on Tue 21 May 2013 06:17:49 PM PDT