Re: Scripps/UCSD geophysicist among international team finding evidence of first plate tectonics


"Aidan Karley" <name1_name2@xxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:VA.00001353.1988cd72@xxxxxxxxxxxxxxxxxxxxxxxxx
In article <Rj0Nh.26037$68.2804@xxxxxxxxxxxxxxxxxxxxxx>, George wrote:
I'm not aware of the argument, not having read a lot of this research.
Perhaps you could enlighten us.

Well, without having time to go back and dig out the papers -

Rosing asserts that the graphite flakes (1) have a significant C-13
enrichment, (2) represent fossilised material from the environment of
deposition of the (now metamorphosed) sediments, (3) are presently
isolated from the environment by being encased in apatite crystals, (4)
the graphite flakes have maintained that isolation since X million years
ago, and (5) that whole-rock dating to about 3600~3800 Ma is valid (IIRC
by Rb-Sr, but I'd have to dig out the papers to check, and I've a
computer to build tonight).

Mozjies disputes that the mineralogy is compatible with separation of
chemicals in a sediment to segregate the carbon; he asserts that there
has been extensive metasomatism of the whole rock which can have changed
the isotopic composition of the carbon at a lower temperature than
necessary to "open" the whole-rock to distort the whole-rock dating, and
he points out that there are crystallographic flaws that reach from the
graphite flakes to the surfaces of the crystals.

Both sides have evidence; both sides have gaps in their evidence. If
there is an answer it'll come form one of two areas : more field work
with better samples and better mapping ; or better technical preparation
such as finer focussing of ion beams in microprobe isotope mass
spectrographs coupled with good optical microscopes and good electron
microscopy.

--
Aidan Karley, FGS,
Aberdeen, Scotland
A light wave is more like a crime wave than a water wave.

Sounds like you and I need to go on a trip to Greenland! Got any grant
money? lol

George


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