Elizabeth Baedke Johnson
James Madison University
Department of Geology and Environmental Science

 

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last modified July 2013

 

Research

Virginia’s Volcanoes: A Window into Eastern North America Mantle Processes

in collaboration with Esteban Gazel and students at Virginia Tech.

 

Few constraints currently exist on the composition and structure of the asthenosphere and lithosphere under Eastern North America Margin (ENAM). Geochemical and petrologic data are critical for interpretation of seismic data in the region and understanding the
long-term, continued evolution of the rift-to-drift transition for ENAM, as well as for rift margins worldwide.


A swarm of Eocene volcanic bodies exposed in Virginia and West Virginia are the youngest known magmatism in the Eastern U.S. and are the only petrologic window into Cenozoic processes in the mantle and lower crust in ENAM. Our project uses these magmas and mantle and basement xenoliths entrained within them to determine the depth, composition and evolution of lithospheric mantle and continental basement under ENAM. We hypothesize that: 1) The asthenosphere under ENAM is composed of enriched primitive mantle; 2) The Eocene magmas were generated through adiabatic melting of shallow asthenosphere (lithospheric delamination, edge-driven convection, or effects from deep subduction) with possible interaction with the lithosphere; 3) Mantle response to the breakup of Pangaea and/or Farallon subduction continues under this passive margin at least through the Eocene; 4) The asthenospheric mantle is relatively wet compared to the extremely dry overlying lithospheric mantle and continental basement; and 5) The lithosphere is inherited from prior orogenic and rifting events and consists of anorthosites, gneisses, and granitoids overlying metasomatized lithospheric mantle.

We will test these hypotheses with an array of geochemical, spectroscopic,and petrologic observations and geochemical modeling. Geochronology of the melts and basement xenoliths will evaluate melting processes, constrain the structure and evolution of the
lithosphere, and evaluate the age of the volcanic activity relative to the age of the xenoliths. Our data will be used to create a vertical cross-section deep into the ENAM.

The EarthScope Transportable Array is currently deployed along the East Coast and the location of our project lies within the Richmond Transect proposed for concentrated seismic studies. Our work will provide important petrologic constraints on basement and mantle composition, lithospheric and asthenospheric structures, and volatile contents for large-scale models of the ENAM constructed from these seismic data.

Our research in the news:

The Washington Post (newspaper)
Hidden Depths: The Mystery of Virginia’s Extinct Volcanoes
http://www.washingtonpost.com/local/virginias-volcanic-past-mole-hill-and-trimble-knob/2012/12/15/175a6d5c-44a6-11e2-9648-a2c323a991d6_story.html?wpisrc=emailtoafriend

The Virginian-Pilot (Norfolk newspaper):
Virginia is for... Volacnoes?
.pdf file

PBS NewsHour (online):
Ancient Volcano Holds Clues to Earth's Deeper Mysteries
http://www.pbs.org/newshour/rundown/2010/11/ancient-volcano-holds-clues-to-earths-deeper-mysteries.html

The Daily News Record (Harrisonburg newspaper):
JMU Digs into a Volcano.
.pdf file

Madison Scholar (online):
What Lies Beneath the Valley's Crust? Local Landmark May Have Answers
http://www.jmu.edu/news/madisonscholar/2010ElizabethJohnson.shtml

Breeze (JMU newspaper):
Making a mountain out of Mole Hill.
http://www.breezejmu.org/news/article_a2a11adc-f052-11df-9500-00127992bc8b.html

 

Selected Past Projects

OH (hydroxyl) in rutile as an indicator of reduction-oxidation conditions in natural samples and piston-cylinder experiments

Magmatic water in Yellowstone mega-eruptions

Feldspars as time capsules of magmatic water content from the 1980-1981 eruptions of Mount St. Helens

Diffusion of hydrogen in plagioclase

The Hope Diamond as a p-type semiconductor