Monturaqui Impact Crater Field Days 2 & 3 (Sat & Sun Dec. 6 and 7)

Sarah and I spent the weekend surveying out to the west of Monturaqui. Our goal for this particular project was to collect a set of samples from the crater out to 3 kilometers to be able to look for microscopic metal and glass spherules generated in the meteorite impact that formed Monturaqui. The impactite contains small metal beads that are thought to be melted meteorite mixed into the glass that is melted target rock (otherwise known as the ground unfortunate enough to be at the site of impact). In this crater, the target rock consists of a thin layer of ignimbrite (an explosive volcanic rock) overlying granite, and last year we discovered that the granite contains veins of hematite, which may provide a terrestrial source for some of the metal found in the impactite. In order to study this in more detail we’d like to have a set of samples of these metal and glass spherules not just from the crater impactite, but also farther away.

To achieve this survey Sarah and I have spent the last two days walking 3 kilometers from the crater, and for every sample site we collect material to take back to the lab to process for glass spherules, and Sarah collects a magnetic sample to try to catch as many of these microscopic metal spherules as possible. This involves moving all the large rocks from a patch of ground about a meter square, running a magnet over that area and collecting that material, then scraping all the rocks off the surface and running the magnet back over to get any more of the magnetic material. Troubleshooting becomes necessary when the plastic bag the magnet is in gets a hole in it, and all that lovely magnetic material sticks directly to the magnet. Our survey was highly successful in terms of collecting sample material, and now the part of science many people might not appreciate is that we have to wait months for the samples to be processed in the lab before we can learn if we have those glass and metal spherules we were looking for. Patience is a good thing to have at times like these.

A good magnet works wonders

Meanwhile, back at the crater Nathalie, Edmond and Carlos have spent an incredibly productive time mapping out and sampling impactite ejecta lobes. Last year we thought ourselves lucky for finding about 30 pieces of impactite during our whole field campaign here. These guys blew that away before lunch the first day of their sampling. We have samples representing the full range of impactite sizes, and have identified and sampled multiple lobes extending down the flanks of the crater. This provides us a great opportunity to do some statistical analysis on the size distribution of the melt fragments in different lobes to look at differences in energy, and extrapolate to the angle and direction the meteorite came from. It’s also a great sample set to look at the chemistry of the melt rocks and see if there are any differences between the different lobes.

Sarah and Monturaqui Impact Crater

Sarah sampling for magnetic material on our traverse

Last, but not least, we were joined by one more team member on Sunday, David Peate from the University of Iowa. I was very happy because David’s my husband and it was lovely to see him again since I’ve been here in Chile for the last 6 weeks doing fieldwork. After more than 30 hours of travelling from snowy Iowa to warm and sunny San Pedro, David is vey happy to be here too and we’re all looking forward to another day at what we’ve come to think of fondly as our impact crater.