[meteorite-list] Platinum is from outer space

From: David R. Vann <drvann_at_meteoritecentral.com>
Date: Fri, 31 Jul 2009 18:12:59 -0400
Message-ID: <1249078379.4a736c6b5431c_at_webmail.sas.upenn.edu>

Of general interest, perhaps - I was researching Komatiites, and ran across
this-
Apparently all crustal platinum is from meteoritic deposits. So, your platinum
wedding band is made of meteorites...

Contact me off-list if you are interested in a copy of this article.

Nature Vol 460|30 July 2009
Progressive mixing of meteoritic veneer into the early
Earth?s deep mantle


Wolfgang D. Maier1, Stephen J. Barnes, Ian H. Campbell, Marco L. Fiorentini,
Petri Peltonen,
Sarah-Jane Barnes & R. Hugh Smithies

synopsis from R&D daily

A research program aimed at using platinum as an exploration guide for nickel
has for the first time been able to put a time scale on the planet's
large-scale convection processes.

The research is reported in a Nature paper titled "Progressive mixing of
meteoritic veneer into the early Earth's deep mantle".

Report author CSIRO Minerals Down Under Flagship researcher Dr Stephen Barnes
said the study group collected a large body of data on the platinum content of
lava flows called komatiites, which host some of the world's major nickel
deposits.

"We found that the oldest komatiites have the lowest platinum content," Dr
Barnes said. "The platinum content gradually increases from about 3.5 billion
years to 2.9 billion years ago. "This tells us that the deep source where the
komatiite came from, down near the boundary between the Earth's core and
mantle, was gradually gaining platinum over time".

The paper's authors now think they know why.

"When the Earth's core formed, it took all the available platinum with it,
leaving the mantle and crust with none," Dr Barnes said.

"Following that, a steady rain of meteorites created the so-called Late Veneer?a
thin surface layer of meteorite debris rich in platinum."

With time through large-scale convection processes, which now cause plate
tectonics, this material was stirred down into the interior of the Earth.

We are seeing the signal of that stirring, which took about 1.5 billion years to
occur. This is the first time a time scale has been put on the stirring, which
has important implications for the people who study the dynamics of mantle
processes and the mechanisms that cause plate tectonics, earthquakes and
volcanoes.

Combined with some other work by the researchers on sister elements to platinum,
iridium and osmium, we also now have a new framework for understanding the
variations in isotopic ratios of osmium with time.

Osmium isotopes are widely used as tracers of mantle processes, but there has
been a mismatch between signals from osmium and from other important isotopic
tracer systems which has eluded explanation until now.

Co-authors Dr Marco Fiorentini and Dr Wolfgang Maier from the University of
Western Australia are delighted that this is a completely academic outcome
which came out of an industry-funded project.

"It is a nice example of an unexpected fundamental discovery arising from a
practical applied science study and demonstrates the very positive
collaborations that exist between CSIRO and the University of Western
Australia," Dr Fiorentini said.
Received on Fri 31 Jul 2009 06:12:59 PM PDT