Geophysical Investigations of the Central Metasedimentary Belt, Grenville Province: Quebec to Northern New York State

Abstract

The correlation of regional aeromagnetic, gravity, and seismic data with geological structures within and along the margins of the Central Metasedimentary Belt (CMB) is used to trace features beneath the sedimentary cover to the south of this major tectonic subdivision. The comparison of geophysics and geology is used to study: (1) the exposed northeast and the covered southwest extensions of the CMB Boundary Zone between the CMB and the Central Gneiss Belt (CGB), (2) the continuation of the Carthage-Colton-Labelle (Mylonite) Zone along the eastern CMB, (3) the enigmatic and seismogenic Clarendon-Linden structure in central Lake Ontario, and its possible continuity as the boundary between the Elzevir, and Frontenac and New York Lowlands terranes and (4) sub-domain boundaries and major internal features.The northern end of a new subdivision of the southwestern Grenville Province, and a prominent zone of plutonic bodies within the central CMB, are identified from distinct aeromagnetic anomaly patterns.The relatively continuous CMB magnetic anomaly pattern, due mainly to shallow lithology and structure, is discordant with respect to gravity gradient belts, due probably to deeper density structure. This discordant relationship, taken together with interpreted Grenville Supergroup thicknesses of 4–5 km (gravity models) and geological and seismic evidence for northwest thrusting in the Grenville basement, may indicate that much of the metasedimentary assemblage is allochthonous.The regional change in mapped structural attitudes, from shallow dipping in the west to near vertical in the east, is in accord with the more direct correlation of potential field anomalies with the geology in the east. Shallower structural attitudes in the western CMB, and displacement of the anomaly-causing density structure at depth, may explain the divergence of the Western Boundary Gradient Belt from the boundary zone outside of the Bancroft to Ottawa River section.The relationship between the CMB and the positive regional gravity field is evident. Greater Moho depth beneath the western CMB-CGB, identified by refraction studies, may indicate that the gravity high reflects a denser lower crust-upper mantle produced by continental collision.KeywordsMagnetic AnomalyBouguer GravityAeromagnetic AnomalyGeological AssociationCanada PaperThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.