MAGNETICS SURVEY OF WESTERN VIRGINIA EOCENE VOLCANIC EXPRESSIONS

Volcanism is normally associated with active plate boundaries, whereas passive margins such as the east coast of North America are typically thought to be geologically calm. The presence of a number of late-Jurassic and Eocene-age volcanic expressions in western Virginia suggest that this assumption cannot be made generally. Extensional forces during the late-Jurassic led to the formation of multiple dikes throughout western Virginia. However, during the Eocene when no known extension or tectonic activity was occurring in eastern North America, several expressions of volcanism, including at least three volcanoes, formed in this region.

Trimble Knob is a felsic volcanic plug situated in a valley in Highland County. Sounding Knob is a mafic-volcanic neck, with at least one known prominent satellite also located in Highland County. Mole Hill is a mafic volcanic plug that cuts through valley floor carbonates located just west of the City of Harrisonburg in central Rockingham County. We intend to collect magnetic data at Mole Hill, Sounding Knob and its satellites, and then at Trimble Knob, in order to develop a stronger understanding of the substructure of these volcanic expressions. It is also our intention to include a brief petrographic study of these sites in order to better understand their magmatic sources. With this knowledge, hypotheses can be developed to describe the conduits in which these expressions reached the surface. Additionally, this information will further advance our efforts to answer the major question as to why these volcanoes and expressions formed in a passive margin.