Monday, 4 May 2009

There will always be just one more sample you will want to analyze, no matter how close the deadline. When this happens, just say no.

Once upon a time, before I started my PhD project, my advisor did some analysis of the mineral monazite in various samples from across Tasmania, to determine the age of the grains. When I started my project some time there after I was unable to obtain training on the use of our microprobe the first year I was here, because our microprobe operator had been hired away to Edinburgh, and it took a while to find a suitable replacement and get him the appropriate visas to start work. So, to keep me out of trouble, in addition to looking at 100+ thin sections of the various Tasmanian rocks that had been collected by previous UTAS students and faculty over the years, to determine which ones would be good candidates for detailed petrological analysis, he also put me to work writing a paper summarizing the results of the monazite dating he’d done before I arrived. For most of the samples I wrote the sample description myself, since I had the thin sections in my office. However, one of them, which had been collected in 1962 from an area which is now under a dam, wasn’t in my office, and my advisor couldn’t find it in his office. Undaunted, I searched the 1962 thesis (which didn’t have a table of contents—so I created one for it) and found the original sample description, and adapted that information for our paper.

Years elapsed. UTAS hired a new microprobe operator. I learned to use the microprobe. I engaged in my own analytical work, both my own monazite dating of other Tasmanian samples, and analysis of other minerals to do calculations as to what temperatures and pressures these minerals must have grown. Eventually, I slowed down on my data acquisition and commenced writing up my results. During this process, I noticed a familiar sample number occurring in the list of “standards” being used for each and every session of monazite dating. Yes, that missing sample from the paper has been living in the microprobe lab all this time. It gives remarkably consistent results. It has had more than 170 different analyses (some samples have had 15), and they all give more or less the same age, and have pretty much the same composition. Indeed, the graphs for its monazite composition show considerably less variation than those for the other samples.

Today it occurred to me that I should look at the sample, to see if I can relate the pattern of its composition to any other details in the sample, so I went and borrowed it from the microprobe lab. Now that I’ve seen it, I so wish I’d have seen it years ago. It is full of lovely albite porphyroblasts with inclusion trails at an angle to the foliation of the matrix minerals. There are tiny garnet grains, and biotite is present. In short, all of the minerals needed to do the pressure/temperature calculations, plus plenty of structural details visible in the sample to make for an interesting story. And here I am, with only three weeks to get my thesis finish, printed, bound, and submitted. There is just no way that I am going to be able to analyze this sample and do the calculations, since I am out of time and budget with which to do it, which is a pity, because it looks as though it would have been a lovely addition to the story.

No comments: