ABSTRACT: Alternating Extension and Contraction in the Proterozoic of the Eastern Midcontinent

James A. Drahovzal, Kentucky Geological Survey, University of Kentucky, Lexington, KY

Previously, the Eastern Granite-Rhyolite Province of the eastern Midcontinent had been understood to be dominantly igneous. Work during the past 10 years has shown that much of the eastern part of the province is actually dominated by sedimentary rocks that are associated with volcanics. Age, stratigraphic, and structural relationships suggest that regionally as many as five major Mesoproterozoic and Neoproterozoic sedimentary sequences have been preserved. Four of these sequences are deposited in rift basins that appear to have been extended between major contractional episodes. The Fort Wayne Rift extensional event (1,325 to 1,284 Ma) was followed by the Elzeverian contraction (~1,240 to 1,160 Ma). The Midcontinent Rift System extensional event (1,109 to ~1,088 Ma) was followed by the Ottawan contraction (~1,090 to 1,025 Ma) and thrusting in that system. The East Continent Rift Basin extensional event (1,020 to ~950 Ma) was followed by the Grenville Front contraction (~950 to 890 Ma) and folding and faulting in the associated rocks. The last extensional event of the Proterozoic (~700 to 600 Ma) was followed by the Louisville contraction (600 Ma). The Louisvillle contractional event resulted in thrusting and inversion of the Louisville Block and about 8 km of overburden being removed. West of the Louisville Block during late Mesoproterozoic, foreland basin rocks were deposited in the English Basin and subsequently eroded by a regional unconformity.

Search and Discovery Article #90907©2000 AAPG Eastern Section Meeting, London, Ontario, Canada