Does the Grenville Front Tectonic Zone Lie West of its Previously Inferred Location in West-Central Ohio?

Mark T. Baranoski¹, Isidore Zietz², Timothy E. Leftwich¹, J. Wright Horton, Jr.², Stuart L. Dean³, and Stephen L. Snyder²
¹Ohio Department of Natural Resources, Division of Geological Survey, Columbus, OH, [email protected], [email protected]
²U.S. Geological Survey, Reston, VA, [email protected]
³University of Toledo, Toledo, OH 43606

The Grenville front tectonic zone (GFTZ), or Grenville deformation front, marks the western limit of Grenville-age deformation in Canada, where exposures have been mapped and studied in detail. At the outcrop near Georgian Bay, Ontario, this tectonic lineament separates higher-grade Grenville metamorphic rocks on the southeast from older, non-metamorphosed and low-grade metamorphic rocks of the Southern Province to the northwest. Starting in the early 1960s, geoscientists have used linear, north-south anomalies on regional aeromagnetic maps to infer a subsurface extension of the GFTZ beneath Phanerozoic cover into Michigan, Ohio, Kentucky, and Tennessee. However in the late 1990s and 2000s, using reprocessed Ohio Consortium for Continental Reflection Profiling (COCORP) OH-1 seismic reflection and sparse deep-well control data, geologists questioned the location of the GFTZ in Ohio as the westernmost limit of Grenville deformation. The term ‘Grenville front magnetic lineament’ was suggested as a substitute for ‘Grenville Front’ in Ohio until ambiguous well and seismic interpretations could be resolved.

In our study digital, composite aeromagnetic maps of the central United States and southern Canada are used to improve the delineation of upper crustal features. Magnetic anomalies delineate the GFTZ in southern Canada, as corroborated by surface geology, and show its southward continuation beneath Phanerozoic cover into Ohio and beyond. In Ohio the revised GFTZ is a crustal-scale feature, characterized by high-amplitude magnetic anomalies on the eastern margin of the granite-rhyolite province. Thus we reinterpret the position of the GFTZ on aeromagnetic maps to lie in westernmost Ohio and eastern Indiana. The new location is west of the traditionally accepted position of the ‘Grenville front magnetic lineament’ in west-central Ohio, which instead may represent additional complexity within the Grenville orogenic belt. We assess the pros and cons of this new aeromagnetic interpretation by comparing deep-well data, seismic reflection data, earthquake history, and Mesoproterozoic/Phanerozoic sedimentary basin architecture. We also consider the implications for basement influence on potential Paleozoic saline reservoirs and cap rocks for industrial-waste and brine disposal, gas storage, CO2 sequestration, and hydrocarbon exploration.

AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012