THE GEOLOGIC FRAMEWORK OF RODINIA IN THE VICINITY OF THE EASTERN TENNESSEE SEISMIC ZONE

The geologic framework of the supercontinent Rodinia is explored in the vicinity of the active eastern Tennessee seismic zone (ETSZ) using results from seismic tomography, potential fields, geochemistry and paleomagnetic reconstructions. Earthquakes in the ETSZ occur in Grenville-age basement rocks located below the southern Appalachian decollemont and most activity occurs SE of a prominent gradient in the aeromagnetic field termed the New York – Alabama (NY-AL) magnetic lineament. The NY-AL magnetic lineament probably represents a major strike-slip basement fault that played an important but enigmatic role in the construction of the supercontinent Rodinia during the Grenville orogony. Recent high-resolution velocity models determined for the ETSZ reveal the presence of a sharp velocity contrast associated with the vertical projection of the NY-AL magnetic lineament that extends to depths of at least 24 km. Anomalously low velocity is present to the NW of the lineament and synthetic velocity models indicate that a probable rock type is granite gneiss. Anomalously high velocity is present to the SE of the lineament; rocks are interpreted to be diorite and granodiorite and have an apparent dip to the SE. Interpretation of the velocity model is aided by recent paleomagnetic reconstructions for Rodinia in which transpressive motion of the Amazon craton is responsible for all of the Grenvillian deformation of Laurentia. Following this reconstruction, the NY-AL magnetic lineament depicts a major basement fault that accommodated left-lateral motion of the Amazon craton during the Grenville orogony in much the same way that extensive strike-slip faults accommodate oblique convergence along active plate margins today. Basement rocks located SE of the NY-AL lineament are interpreted as the collisional remains of Amazonia. This model is in agreement with recent isotopic geochemical studies that demonstrate that the southern and possibly central Appalachian basement is exotic to Laurentia.