ASSESSING THE VIABILITY OF VIRGINIA GEOLOGY FOR GEOTHERMAL POWER PRODUCTION USING MAGNETOTELLURICS

The Eastern North American Margin (ENAM) has experienced much geological activity throughout its history, including two complete Wilson Cycles of rifting and collision, and more recent episodes of volcanism and seismicity. This is reflected in a geology far more complex than it’s status as a passive margin might suggest, and anomalous regions such as the Central Appalachian Anomaly (CAA) centered in northwestern Virginia have been identified. Understanding these anomalies could help constrain the evolution not only of the ENAM, but also of the complex nature of passive margins with active histories more generally.

The CAA is identified as a roughly circular with low seismic velocity at depths of 65-100 km beneath northwestern Virginia, extending into West Virginia. This anomaly has been attributed to lithospheric delamination, or alternatively to the passage of a hotspot in the Cretaceous. Its location is coincident with three different expressions of more recent volcanism; a ~150 Mya (Jurassic) suite of alkaline volcanics, ~48 Mya (Eocene) expressions, and hot and warm springs that are not associated with any particular extrusives but are presumably fed by a magmatic intrusion of unknown provenance.

The purpose of this study is to identify the location of the magmatic intrusion that feeds the warm and hot springs, constrain the areas for which geothermal energy production might be viable, and set the stage for an investigation of the relationship between this intrusion and the Jurassic/Eocene volcanism to the north. 3-D Magnetotelluric (MT) data is collected over the hot springs/warm springs area using a Phoenix Geosystems MTU-5C system, with a spacing of ~12.5 km between stations. The MT data is then combined with existing data from Earthscope MT and inverted using 3D ModEM software.

Preliminary data collection shows clean data to periods of >10^5 seconds imaging depths of >75 km. We anticipate defining the 3-D boundaries and temperature distribution for the source of heat beneath the hot springs/warm springs region, enabling an assessment of the geothermal potential in the region. Furthermore, the work done in this study will serve as a proof of concept for a proposal to evaluate the connection between the hot springs/warm springs and the Eocene/Jurassic volcanism in the region