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Tuesday, 3 November 2015

Banded dolerites on Carningli?


These pics are from the NE flank of Carningli, close to the entrance passage leading into the hill fort, and the rocks look to me like banded dolerites.  Not my area of expertise, but I don't think they are andesites, or dacites, or rhyolites.  The GS map for the area shows dolerites and gabbros -- but this doesn't look like a gabbro either.  Over to the experts?  Suggestions, anybody?  The little strips that stand proud seem to be very narrow quartz layers.....





Just added:  here's another photo found on my file.  It shows some bands transverse to the others.  Does this mean that the bands of quartz (?) are secondary features, due to precipitation along bands of weakness or fractures in the rock a long time after cooling?


PS.  I stand corrected -- this post referred originally to "banded dolerites" but it appears that there are no such things.  So "banded" will probably be OK, since that's simply a descriptive term that makes no assumptions as to origins.


2 comments:

Myris said...

Do not know. Knock a piece off and post.

Flow banding in the sense you are using it is not possible in dolerites, they are by definition (high level) intrusives. Need to see it in the flesh.
I think were they 'flow-banded dolerites' they would be in the geological literature and I do not recall any such writing.
M

BRIAN JOHN said...

Thanks Myris -- I thought I saw the term somewhere. Maybe just for rhyolites? Anyway, next time I go up I'll try to bash a bit off for you to look at....