Tuesday, May 1, 2012

Wow, it's been a month since my last blog post.  Ever get the feeling time is passing slowly while you're just doing what you're doing, yet quickly at the same time when you stop a moment and reflect?  The past month, I've been following more or less the same daily routine.  I started waking up earlier and making a "real" breakfast (by that I mean, eggs, toast, sometimes bacon).  I find that it's helping, and makes me feel more physically balanced during the day.  Then I get to school around 9:30, and start the day by either reading a paper or two, or working on calculations or data analysis.  That usually goes on until noon, when I eat lunch.  Then a couple more hours of "real" work, and then I pick minerals from 3 pm till closing time, 5:30 or so.  It's tedious picking minerals, but it's a satisfying feeling when you get a small pile of beautiful emerald green, pure cpx grains.  Garnets are difficult to pick, not because there are few, but because most of the garnets I encounter are heavily kelyphitized.  It's rare that I find a perfect, pink grain with no kelyphite, but it makes my heart skip a beat almost when I do find one!  I'm working on a method to try to remove the kelyphite, but if worse comes to worse, I have 70 grams more of this particular sample, so I could pick almost all of it for the purest garnet. So, although the mindless lab work takes up so much time, I know in the end it will hopefully amount to something very interesting (in this case, Lu-Hf and Sm-Nd dating of the Sierran pyroxenites). 

I've also thought more about my Sierran refertilization project, and honed down my sloppy first hypotheses to a better working one.  Initially, I wanted to determine what kind of melt precipitated the metasomatic generation of cpx and garnet, similar to what people working on cratonic xenoliths have done.  In their case, their xenoliths are hundreds of degrees hotter than mine (~1000 C or more, compared to 750 C for the Sierran xenoliths), so in theory, less subsolidus re-equilibration has taken place and the metasomatic minerals might better retain a signature of the melt from which they crystallized.  In the Sierran case, everything has undergone subsolidus re-equilibration, probably obliterating any original melt imprint.  So, the problem is that individual minerals in the Sierran xenoliths are all out of disequilibrium because they've cooled and exsolved other phases like garnet.  The only hope is to look at the whole rock compositions, which is what I'm doing next, with some new data to come in the next few weeks.

I've also been practicing with my new camera more, and resurrected my old Flickr account which I started in 2009 but never used extensively until now:

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