Tuesday, September 9, 2008

Field work

It has actually been awhile since I last posted a blog and I finally got to my field area. The above picture is after eating lunch in Anderson, CA at a Panda Express. I was laughing at the view, not many fast food joints have such a great view, so I figured the picture was a great way to start out the trip! If you want to know where Lassen Peak is look above my head. I was hoping that Lassen was not going to be busy and it wasn't. The weather was beautiful and the sky a wonderful blue color. So we set up camp and embarked on my reconnaissance trip of my field area.

So when we got there Wednesday afternoon, we didn't really have a plan, so we decided since I had not hiked the Chaos Jumbles in detail, that is what we would do first. A refresher, in case you forgot from previous posts, the Chaos Crags are six dacitic domes, named A-F, with Dome A, the oldest in age. The Chaos Jumbles were the result when Dome C collapsed somewhere around 300 years ago (Heiken and Eichelberger, 1980). For my field work, I am trying to figure out the magma mixing event or events. To do so, I need to look at the enclaves (blobs in the rock not of host origin) and distinguish if there are different types. So far there seems to be three different types present in each of the six domes, but I believe that there might be more variations. I think I will be able to determine this with more field work and Crystal Size Distributions (CSD).

The above picture is a fine-grained porphyritic enclave in the host dacite, as classified by Heiken and Eichelberger, 1980. The enclave is about 1 ft long, the larger crystals are resorbed plagioclase from the host dacite.

This is a medium grained porphyritic enclave also in the dacite host and once again the larger crystals are resorbed plagioclase. This enclave was smaller at around 8 in.

Heiken, G., and J.C. Eichelberger, 1980, Eruptions at Chaos Crags, Lassen Volcanic National Park, California; Journal of Volcanology and Geothermal Research, 7, 443-481.

There is still more from the first day, but you have to wait until the next post.

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