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

From: Count Deiro <countdeiro_at_meteoritecentral.com>
Date: Tue, 21 May 2013 17:31:03 -0700 (GMT-07:00)
Message-ID: <18318149.1369182663704.JavaMail.root_at_wamui-haziran.atl.sa.earthlink.net>

Thank you, Bernd. You are a river to your fellow enthusiasts.
Guido

-----Original Message-----
>From: Richard Montgomery <rickmont at earthlink.net>
>Sent: May 21, 2013 5:21 PM
>To: "Bernd V. Pauli" <bernd.pauli at paulinet.de>, meteorite-list at meteoritecentral.com
>Subject: Re: [meteorite-list] Chelyabinsk - slickensides or shock planes?
>
>Bernd, perfect summary. Thanks.
>
>
>----- Original Message -----
>From: "Bernd V. Pauli" <bernd.pauli at paulinet.de>
>To: <meteorite-list at meteoritecentral.com>
>Sent: Tuesday, May 21, 2013 2:36 PM
>Subject: [meteorite-list] Chelyabinsk - slickensides or shock planes?
>
>
>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 08:31:03 PM PDT