Archive for July 18th, 2017

High-Temperature Geochemistry in Action

July 18th, 2017

WOOSTER, OH – Over the last couple of weeks, our Keck Geology Team Utah has been hard at work in the College of Wooster Geology labs. We collected a dozen samples from Ice Springs Volcanic Field in the Black Rock Desert, Utah to understand the eruption history and the age of the lava flows.

The first processing step is to powder the sample. Addison Thompson (’20, Pitzer College) uses the rock saw to isolate pieces of fresh rock.

Addison and Madison Rosen (’19, Mt. Holyoke College) use a sledge to break the sawn pieces into smaller bits.

Sam Patzkowsky (’20, Franklin and Marshall) cleans the chips so that we can crush them in the shatterbox.

Emily Randall (’20, College of Wooster) sieves the powder and makes sure all of it is small enough for the next step. We sent some of this powder to the Purdue PRIME Lab, where they’ll measure the abundance of 36Cl in our rocks.

Pa Nhia Moua (’20, Carleton College) pulls samples out of a red-hot oven so that we can measure Loss on Ignition (LOI) to determine how much H2O might be in the samples.

Sam and Addison weigh out accurate amounts of the oxidized sample and flux, which lowers the melting temperature and helps our samples melt so that we can make glass discs.

The samples get melted in the fluxer and poured into molds to make glass discs.

The glass discs are loaded in the XRF and analyzed for their major element chemistry. We use the chemistry along with the data from Purdue and the location and orientation of the sample to calculate an age for the lava flow.

We’re using another method called Varnish MicroLamination (VML) dating to provide an independent estimate of the age of the lava. Desert varnish is a dark coating of clays and iron- and manganese-oxides that accumulates on the surface of samples in arid environments. You may have seen ancient petroglyphs carved into the desert varnish. Researchers use the layering in VML to date pieces of rock art. In order to use the VML method, we have to make ultra-thin slides of our rocks so that we can see through the varnish.

Addison pours epoxy into plastic molds to mount the VML samples.

Pa Nhia has been sanding her VML sample for days to grind it to the correct thickness without grinding away the varnish. It’s dirty, delicate work.

By the end of the week, we should have age estimates for the lava flows and a better idea of the sequence of eruptive events that formed Ice Springs Volcanic Field. Check back later for our GSA abstract!