[meteorite-list] Continuing education Friable Slickensides

From: Mr EMan <mstreman53_at_meteoritecentral.com>
Date: Sun, 22 Jun 2008 03:48:05 -0700 (PDT)
Message-ID: <115832.29943.qm_at_web55206.mail.re4.yahoo.com>

Well Pete, Friable of course are eggs 'n bacon... And slickensides come from the bacon grease... Ok-- couldn't resist.

Friable: in the geological sense, means brittle to the point of being easily crumbled. This is the term we use to describe rock "fabric" which is so poorly consolidated, poorly cemented, or extensively exsolved, that it can be crushed with the strength of one's hand. Burbojole(sp) is a classic friable meteorite which was recovered from several meters of mud underneath sea ice. Amazing integrity for such penetration, it would seem. Did Carancus become friable as a result of impact? The tenstile/crushing test were quiet variable( 2-62Mp) I haven't seen the thin section studies.

Slickenside: A structure/zone that lies on/between a fault/slippage face which may be striated, grooved, polished or, all of the above. It may contain "rock flour" or secondary minerals from the physical, then chemical, alteration of the zone. The term adopted from the german use. What I believe I know about slickenside formation is that it is a lengthy process" both in time and displacement. (? few minutes to seconds vs ? few miliseconds).

The conclusions in the Carancus report, if true, might tend to lessen the difference between formations of slickensides and shock veins. Who am I to challenge a peer-reviewed publication---but I have reservations. Remember it was not a lot of physical analysis so much as computer modeling.

 I still don't see a shock veins forming striations, owing that their primary forming process was hitherto understood to be pooling of flash-melted olivine shifting to the high pressure polymorph: ringwoodite under mantle level pressures(as an example). PDF--planar deformation features aka shocked quartz was recovered from the impact soil but those can form and far lower pressures then needed to form ringwoodite.

  Seems almost every piece I saw had slickensides and unless there was a sampling error, I also have reservations that Carancus was not extensively chocked full of slickensides at entry. (See also Zag A for slickensides) Fragmentation seemed to slightly favor rupturing along slickensides but breaking across them was common also. If they had they formed at impact, seems they would all have favored breaking along the slickenside surfaces.

 Do the slickensides of Carancus contain glass, indicating that they could have healed the surfaces giving back some strength? (There is a Doctorial thesis in thee somewhere). Dating the slickensides would also shed light on whether they formed at impact or in some past collision on a parent body.

If there was no containment--as in a disintegrating mass, then seems to me that there would be no slipping-- just crumbling. I would like to see some research on the composition and structure of the slickensides to know how old they were and how hot the faces got. Weighing what we know, they are old not new.

Funny but it is conceivable that the Carancus slickenside could represent a unique internal fusion ahem crust..er feature.

Elton


--- On Fri, 6/20/08, Pete Shugar <pshugar at clearwire.net> wrote:
> Can someone please define for me the two terms: friable and
> slickensides?
> Thanks, Pete
Received on Sun 22 Jun 2008 06:48:05 AM PDT