Thursday, January 15, 2009

Always double check!

I collected most of my samples for my PhD project in March of 2006, consequently their field numbers start 06___. Those samples all came from the northern fault block of the Collingwood River Metamorphic Complex. In November of 2007 my advisor and I did one additional trip, to the southern fault block of the Collingwood River, in search of the long-lost Tasmanian whiteschist. We found it, and collected a number of other samples from the area as well. Whilst we were out, we also stopped by the northern block and picked up another couple of oriented samples, just for good measure.

In October of 2008 we decided that there was just enough funding left to do some detrital zircon dating for two samples from the Collingwood River. I was told to select "sandy" samples as being most likely to contain zircons. So I picked out half a dozen from both the northern and southern blocks of the Collingwood River which were sandier than the others, though not necessarily sandy enough, and brought them along to my lesson on rock crushing. My teacher du jour narrowed it down to three likely candidates, two with 06___ numbers, and one with a 07___ number. So we, thinking that there might be value in having one from each fault block, chose one of each and we commenced crushing.

Since then I've been thinking in terms of having crushed one from each fault block, so was not too surprised when their detrital zircon patterns were somewhat different from one another. Today, at long last, I decided to make the figure showing the location these two samples were collected from. Yup, you guessed it. They are both from the north block! They were collected from locations not more than 250 meters apart from one another along the highway.

However, since the other 07___ samples were all rejected as not being sandy enough to bother, I can't really complain that I don't have one from each block. There is just that lingering embarrassment that one gets when one realizes that the assumption under which one has been operating doesn’t actually apply. The best cure for that? Admit the mistake publicly—then it won’t ever be repeated!

And always consult the map...

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