Bernd, perfect summary. Thanks.
----- Original Message ----- From: "Bernd V. Pauli" <bernd.pa...@paulinet.de>
To: <meteorite-list@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 ______________________________________________ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list ______________________________________________ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
