[meteorite-list] Chelyabinsk - slickensides or shock planes?
Richard Montgomery
rickmont at earthlink.net
Tue May 21 20:21:51 EDT 2013
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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