Relationship Between Precambrian Basement and Paleozoic Structure on Northeastern Flank of Michigan Basin

John D. Herman

Extensions of boundaries of three major Precambrian provinces exposed immediately north of Manitoulin Island, Ontario, Canada, were traced southwestward beneath Paleozoic rock cover by interpretation of magnetic data images. Paleotopographic relief on the surface of the buried Precambrian provinces was inferred from study of topographic maps and digital elevation data over areas where these rocks are exposed just north of the island. On the eastern half of Manitoulin Island, the southern extension of the lower Proterozoic Southern province, which is buried by Paleozoic units, is characterized by narrow, linear, low-amplitude, nearly east-west-trending positive and negative magnetic anomalies. As a whole, the buried portion of this province is associated with a relatively road northeast-trending structural arch mapped at the Ordovician Trenton-Black River level. Locally, the east-west-trending negative magnetic anomalies are interpreted to trace quartzite ridges on the Precambrian basement surface equivalent to the lower Proterozoic Lorraine or Bar River formations. These negative anomalies also follow narrow east-west-trending anticlinal structures mapped at the Trenton-Black River level. These structures probably formed by differential compaction over the quartzite ridges. The Southern province is bounded on the southeast by middle Proterozoic granitic intrusives of the Eastern Granite-Rhyolite province. These intrusives are associated with northeast-trending, low-amplitude positive and negative magnetic anomalies. Further southeast, the Eastern Granite Rhyolite province is separated from upper Proterozoic high-grade gneisses of the Grenville front, which is characterized by prominent, northeast-trending positive magnetic anomalies. Subtle, northeast-trending Trenton-Black River synclinal structures were mapped along the boundaries between these three Precambrian provinces using well-log data. Explanations for the cause of these synclines include differential compaction over paleovalleys along the basement province boundaries and reactivation of faults separating the provinces.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.