Professor Cousens Completes Field Work in Nevada

Friday, July 24, 2015

Map of Nevada showing calderas of the Ignimbrite Flare-up outlined in yellow.  Note Stillwater Complex, including Elevenmile Canyon caldera, on the west side of the flare-up area.  Map from Henry and John, 2013, Magmatism, ash-flow tuffs, and calderas of the ignimbrite flareup in the western Nevada volcanic field, Great Basin, USA.  Geosphere v. 9, p. 951-1008.

Map of Nevada showing calderas of the Ignimbrite Flare-up outlined in yellow.  Note Stillwater Complex, including Elevenmile Canyon caldera, on the west side of the flare-up area.  Map from Henry and John, 2013, Magmatism, ash-flow tuffs, and calderas of the ignimbrite flareup in the western Nevada volcanic field, Great Basin, USA.  Geosphere v. 9, p. 951-1008.

 

Professor Brian Cousens recently returned from doing field work in Nevada. He was accompanied by one of his Honours students, Ayesha Landon-Browne. Also on this trip were colleague Jonathan O'Neill (University of Ottawa) and his Master's student Dan Stepner. 

See below Professor Cousen's detailed account of his trip: 

Along with colleagues at the US Geological Survey and the Nevada Bureau of Mines and Geology, we are investigating the geochemistry of caldera-related pyroclastic rocks in northwestern Nevada.  The focus of field work in May of 2015, and the subject of Dan Stepner’s MSc thesis, was on the 25.1 Ma Elevenmile Canyon caldera located in the southern Stillwater and Clan Alpine Ranges near Fallon, Nevada.  The Elevenmile Canyon caldera is the youngest of three caldera complexes in the area that are a major part of igneous activity in this region from ~ 30 Ma to 24.8 Ma.  Great Basin faulting and deformation has broken the caldera into tilted blocks that nicely expose the stratigraphy from the pre-caldera basement rocks up to some erosional level below the top of the pyroclastic sequence.  Dan’s work, co-supervised by Cousens (Carleton University) and O’Neill (University of Ottawa) with field support from David John, Joe Colgan, Kathryn Watts (USGS) and Chris Henry (NBMG), will attempt to establish geochemical gradients or changes within the pyroclastic rock sequence and relate this to the state of the Elevenmile Canyon magma chamber during eruption and emplacement of the rocks.  Ayesha Landon-Browne will complete a BSc Honours thesis on the Pb isotope geochemistry of potassium feldspar phenocrysts in the Elevenmile Canyon tuffs.

 

Dan Stepner collecting samples with David John (USGS).

Dan Stepner collecting samples with David John (USGS).


Recent snow accumulation in the Toiyabe Range, east of the study area.  Snow was an issue more than once during field work.  Gorgeous view from the Clan Alpine Range.

Recent snow accumulation in the Toiyabe Range, east of the study area.  Snow was an issue more than once during field work. Gorgeous view from the Clan Alpine Range.


Abundant rhyolite pumice in Elevenmile Canyon tuff.  Pumice is the sampling material of choice, since it is composed entirely of magma.

Abundant rhyolite pumice in Elevenmile Canyon tuff.  Pumice is the sampling material of choice, since it is composed entirely of magma.


Poorly-developed, but obvious, columnar jointing in Elevenmile Canyon tuff.  Pyroclastic layers are dipping to the left (east), and the joints are perpendicular to the contacts between tuff units.

Poorly-developed, but obvious, columnar jointing in Elevenmile Canyon tuff.  Pyroclastic layers are dipping to the left (east), and the joints are perpendicular to the contacts between tuff units.


Dan collecting a sample and taking notes.

Dan collecting a sample and taking notes.


Dan and Jonathan looking for the best, freshest rock with pumice!

Dan and Jonathan looking for the best, freshest rock with pumice!

Our home for field work, Middlegate Station.  "Rustic" is the best term for this motel/bar/restaurant/gas station.  The food is awesome.

Our home for field work, Middlegate Station. "Rustic" is the best term for this motel/bar/restaurant/gas station. The food is awesome.