[meteorite-list] Slickensides vs. Shock Veins..was Nice photos of Carancas Meteorite

From: dellenit at aon.at <dellenit_at_meteoritecentral.com>
Date: Thu, 04 Oct 2007 08:23:52 +0200 (CEST)
Message-ID: <1191479032.470486f8664e0_at_webmail.aon.at>

Hi Elton,

you are right with the slickensides. But some comments on Maskelynite:
It is NOT from olivine ! it is a glassy mineral which has a composition of plagioclase feldspar. It results from quenching from shock induced melt !
ref: http://www.lpi.usra.edu/meetings/metsoc99/pdf/5047.pdf

Harald


----- Original von: Mr EMan <mstreman53 at yahoo.com>:

> Hello Graham,List and-- Expeditionary Members,
wherever you are....

 It is an easy mistake in the broad scheme of things
but the striation features in these photos are not
shock veins but slickensides. Slickensides are the
slippage surfaces of micro/macro faults where each
side is ground down in a natural milling process.

In terrestrial geology, they may be filled with any of
several clay sediments-- some of which includes
melt/fusion particles (Google "slickenside" to see
that there is a book's worth of information that
slickensides can reveal about rock and soil dynamic
history. One branch of my collecting is assembling
and cataloging slickensides samples and
locations..self gratuitous grin inserted here)

Slickensides accumulate a rock flour-like debris which
tends to lubricate and as a demarcation of chemical
and physical bonding between opposing surfaces-- it
keeps the adjacent sides from cementing. Unhealed,
they are natural lines of weakness. It makes perfect
sense that on one of those fragments pictured late
flight fragmentation shows a secondary fusion on a
preserved slickenside: probably a rare, even unique
surface feature as I know of no other example
preserved outside of post flight/ground impact
fragmentation. (e.g. Zag)

Shock veins on the other hand, are filled with the
mineral maskelynite which is the ultra compact spinel
form of olivine. It forms in very high pressure
environments such as asteroid collisions/shock events
or deep within planets. Maskelynite is one of the
major mineral forms in deep mantle here inside Earth.

 In meteorites, the shock vein acts to cement the
sides together ceramically--known as a "healed"
fracture, it becomes stronger and less likely to
fracture along the shock vein itself.

Elton

--- ensoramanda <ensoramanda at ntlworld.com> wrote:
> This looks like the real thing when compared to
> others I have seen or heard discribed.
>
> Any comments about the features welcome.
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Received on Thu 04 Oct 2007 02:23:52 AM PDT