Summer Crushing

Hello all! This summer I am back at Denison working on a project with Professor Erik Klemetti involving the magmatic evolution of the Lassen volcanic system in Northern California. Lassen is the southernmost volcano in the Cascades Range and has had eruptions as recently as 1915. Our goal is to analyze the zircon minerals that we extract from various samples representing different eruptions and phases of the system. We hope to have a better understanding of the composition, interactions, and overall evolution of Lassen’s magmatic system from this project. To get to the zircon, however, much pounding, sorting, and separating must take place.

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The lab.

Thus far, I have been focusing on samples from Eagle Peak which are 66 ka (thousand years old) and are relatively young. Using a stainless steel mortar and pestle I have crushed the rhyolite and sorted the grains by size using sieves- and a fair amount of physical labor. I then cleaned the portion of grains that contain the accessible zircons using water, ethanol, and pure water in varying stages. These samples were then left to dry whereupon I began to remove the heavy magnetic material, particularly the stainless steel fragments from the crushing process, using a hand magnet used by prospectors. The next step involves a rather persnickety piece of equipment called the Frantz (more magnets) and then on to separation of the zircon by either heavy liquids- a more efficient and clean but time consuming process- or the gold table which is less efficient but produces high yields quickly. Ultimately these zircons will be dated and analyzed by the SHRIMP-RG ion microprobe at Stanford.

http://shrimprg.stanford.edu/

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The separation process: the magnet picks up large magnetic fragments (left sheet of paper) from the sample (right sheet of paper).

In the meantime, I have been crushing, sieving, washing, and separating samples from Chaos Crag and the 1915 Lassen eruptions. While these samples have been previously analyzed, we wish to do a rim analysis on them to better understand the magmatic environment during their last stages of growth before eruption. Check back for more updates!

 

Liz Bertolett