date of cooling of igneous dikes

Post date: Jul 26, 2013 5:51:58 PM

I switched mentors a few weeks ago, and now I am working with Marty Grove on a similar project that concerns finding the date of cooling of igneous dikes that cut across folds in the white /inyo mountains. Why is this important? Simply because no one knows yet.

So we've managed to extract a few dozens of zircon grains from a fist-sized rock sample from the white mountains by first crushing, then sieving by density on a gold-panning table (Gemini Table), then removing magnetic particles through the Frantz, sieving by density again with super dense, toxic methylene iodide, and finally extracting zircons manually through needles under the microscope.

The gemini table: The grains flowing out of the groove are dense.

The Frantz - removing magnetic particles (Zircon is not magnetic)

Methylene Iodide - Sieving again by density

Mounting grains - Done by hand under a microscope. The process is surprisingly tiring and you need a good eye to spot zircons which are usually 4-sided, slightly yellow, and very shiny due to its high index of refraction.

We mount the zircons on a sticky tape, then harden a mold of epoxy onto it. Next step is polishing the epoxy mold into a smooth surface with sandpaper and diamond grit, then coating with conducting carbon or gold and sticking the mount under the Scanning Electron Microscope (SEM).

Rotating disk - used in combination with diamond powder to polish grain mounts

Zircons under a Scanning Electron Microscope

Unfortunately, everything I put on my mount consisted of apatite and a bit of quartz.

But I certainly have learned a lot about the U-Pb radioactive dating process.