The recent magnitude 5.8 earthquakes in Mineral, VA, impacted major metropolitan areas on the East Coast of the U.S. and sparked a need to better understand the geologic characteristics the of Eastern North America Margin (ENAM). A group of more than 100 volcanic bodies approximately 47-49 million years old exposed in Virginia and West Virginia are the youngest known eruptions on the East Coast of the U.S. These magmas and the fragments of rock they collected from the crust and mantle during their ascent and eruption are the only direct samples of the crust and the mantle in recent geologic times. The results from this study will be used in conjunction with data from the EarthScope Transportable Array of seismometers currently being deployed along the East Coast as well as other seismic studies to create a comprehensive picture of the state of the crust and mantle underneath the Eastern U.S., providing context for the potential of future seismic hazards. This project will support graduate and undergraduate research at Virginia Tech and James Madison University. The proximity of the field site to both universities makes field characterization and sampling highly accessible. A field trip for middle and high school students and an outreach course through the Lifelong Learning Institute will be developed in addition to course materials for general education. An exhibit will be created for the Museum of Geociences at Virginia Tech. Data from this research will be shared with the public, the GeoPRISMS and EarthScope communities.
Few constraints currently exist on the composition and structure of the asthenosphere and lithosphere under the 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. We hypothesize that: 1) The Eocene magmas were generated through adiabatic melting of shallow asthenosphere (e.g., lithospheric delamination, edge-driven convection, or effects from deep subduction), 2) Melting is related to the lithospheric response to the breakup of Pangaea and/or Farallon subduction that continued under this passive margin at least through the Eocene. We will test these hypotheses with an array of geochemical, spectroscopic, and petrologic observations and 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. The EarthScope Transportable Array is currently being deployed along the East Coast through 2013 and the location of our project lies within the ?Richmond Transect? proposed for concentrated seismic studies. Our data will produce a vertical cross-section deep into the ENAM that will provide important constraints on basement and mantle composition, lithospheric and asthenospheric structures, and volatile contents for large-scale geodynamic and seismic studies.
