A SEISMIC EXPERIMENT TO INVESTIGATE MAJOR CRUSTAL-SCALE STRUCTURES IN EASTERN KENTUCKY AND TENNESSEE

With the completion of the EarthScope project in the central and eastern United States, intriguing crustal-scale issues remain unanswered. For example, contrasting interpretations of the East Continent Gravity High (ECGH) highlight unresolved first-order questions related to the assembly of Rodinia. The ECGH has been interpreted as a crustal-scale, dense, highly magnetic body related to intra-Grenville rifting, and for some researchers, delineates the Grenville Front (GF) in eastern Kentucky and Tennessee. However, recent EarthScope-related investigations associated this body with the Midcontinent Rift (MCR), based largely on similarities between Bouguer gravity profiles across the ECGH and those across the traditionally mapped MCR farther north, which contrast with gravity profiles across the exposed Grenville Front in Ontario. Well samples from the top of basement in the ECGH contained metamorphic rocks, suggesting that if the anomaly is rift related, its source must be deeper in the subsurface, below rock metamorphosed during the Grenville Orogeny.

The New York-Alabama Magnetic Lineament (NAML), southeast of and nearly abutting the ECGH, is a candidate for the suture zone formed during the assembly of Rodinia, as suggested by recent tomography and electrical conductivity studies. Further, the Kentucky Magnetic Anomaly (KMA), the strongest satellite-altitude magnetic anomaly in the western hemisphere, is also intertwined in this continental architecture.

To fill in critical knowledge gaps, we suggest that a high-resolution active- and passive-source seismic experiment, featuring a ~250-km-long large-N linear array and a complementary lateral grid that traverse the GF, ECGH, NAML, and KMA would facilitate constraining the locations and geometries of these structures and their relationships to the MCR and Grenville Orogeny. The linear array would consist of three-component geophones, which would be used to image crustal structures via reflections and refractions from Vibroseis and explosive sources and via high-frequency receiver functions. Broadband receiver functions from the coarse lateral array would be used for validating those determined by the linear-array and for evaluating out-of-plane, 3-D effects.