[Phys-L] Re: Age of Zircon

[Brian Whatcott <betwys1@SBCGLOBAL.NET>]

At 12:26 AM 4/9/2005, you wrote:
> The U Wisconsin allegedly has a speck of zircon about 4.4 billion years
> old? The size of the speck is of the order of magnitude of a couple of
> human hairs.

> Where did this speck come from? ie how was it discovered?
>
> How do they know it is zircon?
>
> How was its age measured???
>
> Jim

 From a Geo432 slide at UIUC site...

"Zircon is found as an accessory mineral in most
igneous, metamorphic and clastic sedimentary
rocks. The resilience of zircon to survive high grade
geological events combined with its high
uranium and low common lead initial contents
make it a unique chronometer to investigate
the history of the Earth's lithosphere. Zircons
are the only solid remnants of the earliest
period of Earth evolution (>4 Ga) and therefore
they are the sole witnesses to the birth of
continental crust and hydrosphere on Earth.
The U-Pb analytical data obtained in zircons
are essential to integrate the evolution of
igneous, metamorphic and sedimentary rocks
in an absolute time framework, as they provide
first order constraints on the age, duration and
rate of the events involved in the genesis of a
given rock."


from the NewWave Research website offering at

  <http://www.new-wave.com/1nwrProducts/LAzirconAPP.htm>

Zircon Dating - 213nm versus 266nm Nd:YAG Lasers


"The technique of U-Pb zircon dating by LA ICP-MS was
developed using the fourth harmonic wavelength of a Nd:YAG
  laser at 266nm. It was evident that there were some difficulties
with this method including short ablation signals and signal instability.
Technological advancements by New Wave Research have enabled
  the use of the fifth harmonic wavelength at 213nm in laser ablation.
This wavelength has improved significantly not only signal duration
  but also signal stability. As both factors are important in isotope
  ratio measurements, it was expected that U-Pb dating of zircons
  would benefit greatly.

The longer, more stable signals of the 213nm system give rise to
  lower errors and therefore more precise data. Over several
  individual determinations the 213nm data are consistently
more accurate than the 266nm data. "



Brian Whatcott    Altus OK    Eureka!
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