Re: Geology Question (KRS related)


"Hayabusa" <peregrine@xxxxxxxxxxx> skrev i meddelandet
news:kme7u1tdlnnav9o9vijsg3h11i3a151ceb@xxxxxxxxxx
On 1 Feb 2006 23:06:58 -0800, "Daryl Krupa" <icycalmca@xxxxxxxxx>
wrote:

Daryl: I appreciate your knowledge, and I'm glad there is more than
one geologist around here, but simply judging by style, I feel you
have a propensity to make things more complex than they are. From the
description, the KRS is a fairly straightforward rock (geologically
speaking). The properties are distinctive, and I believe, and I
suppose you would agree, that a colleague who is closely familar with
the region would be able to pinpoint the location of origin of the KRS
within a couple miles or dozen miles. With some experience, rock
fabrics are as distinctive as the grooves on your thumb. Here in my
city there is a shop with a floor made of marble of which I am
positively sure it can come only from one particular quarry in Austria
(1000km away)

fkoe:
I tend toward the submarine-avalanche-of-unstable-accumulations-
of-unstable-continental-slope-deposits-derived-directly-from-
rapidly-eroding-volcanic-highlands proto-melange scenario, myself.

fine with me. I have seen turbidite deposits (graywacke) in ultramafic
archaic sediments in Zimbabwean greenstone belts which are commonly
interpreted as graben structures which were only a couple kilometers
across. Except for the bulk chemistry, these were perfectly good
graywackes.


By "the rock", do you mean the KRS in particular, or are you
making a generic reference to metamorphic rock?
If the former, I might be moved to argue that jointing, and/or
cleavage, has been more influential upon its shape and splittability.

The krs. And I still think the layer-parallel cleavage is the most
characteristic feature of the rock.

also indicating
a significant direction of stress on the rock during metamorphosis.
It might be the elongated grains, but then we have to guess at
what words are missing to connect
"The elongated grains" to
"composed of various mica minerals".

That goes without saying.

I'm sorry, it is not obvious to me what it is that need not be said.
Could you say it, please?

Ever looked into a thin section?

eeYehhhhhsss ...

--- umh - excuse me for being condescending. I shouldn't have done
that.

The only other mineral that could line up because of shape
elongation would be the first amphibolites, but for them
the metamorphic temps were not high enough, apparently,
or else they would have been mentioned.

I'm sorry: "only other mineral" than which mineral, please?
Keep in mind that I was talking about "elongated [detrital]
grains", not "micas".
I have not yet been convinced that "elongated grains" is
intended to refer to micas.

Whether or not, it doesn't matter because detrital micas are _always_
aligned with the bulk foliation (in this case: the sedimentary
layering). There are no micas with a low aspect ratio, and during
compaction they align even more. (They might be mildly chlorizited,
btw.)

I think that a geochemical study of the surface minerals, a SEM and an
xray diffraction of the surface micas should show if the micas are
relatively fresh or not.

That type of study was made and the surface micas showed that it wasn't
fresh or relatively fresh at all.

Inger E

A difference of nearly 1000 years should be
recognizeable.


fkoe



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Relevant Pages

  • Re: Geology Question (KRS related)
    ... the mineralogy of the KRS and states: "The elongated grains exhibit a preferred orientation that is sub-parallel with the foliation composed of various mica minerals that comprise the matrix." ... a significant direction of stress on the rock during metamorphosis. ... It might be the elongated grains, but then we have to guess at ... "composed of various mica minerals". ...
    (sci.archaeology)
  • Re: Geology Question (KRS related)
    ... With some experience, rock ... It might be the elongated grains, but then we have to guess at ... "composed of various mica minerals". ... it doesn't matter because detrital micas are _always_ ...
    (sci.archaeology)