TECTONIC AND METALLOGENIC IMPLICATIONS OF ARCHEAN AND PROTEROZOIC UPPER MANTLE AND DEEP CRUSTAL FEATURES IN BASEMENT TO THE GRENVILLE PROVINCE IN E CANADA AND NORTH-EASTERN USA

Components of aeromagnetic data, its derived pseudo-gravity, and satellite gravity disturbances, extracted by frequency domain filtering, portray regional structures at different crustal and upper mantle depths in the Grenville Province. This study highlights the influence such basement features have played on deformation of overlying allochthonous terranes and the formation of mineral deposits.

Satellite gravity and enhanced pseudo-gravity images clearly show that NNW-SSE structures of the Paleoproterozoic SE Churchill Province continue beneath allochthonous terranes in the NE Grenville, confirming seismic interpretations. The jigsaw puzzle-like fit between subcontinental lithospheric mantle (SCLM) domains along the central to eastern Grenville boundary with the Archean Superior and SE Churchill provinces is interpreted as a Labradorian (ca. 1.7-1.6 Ga) rift likely formed in a back-arc setting, reactivating ca. 2.2 Ga extensional structures paralleling the SE Superior margin. An Archaean age is, however, interpreted for SCLM domains beneath the SW Grenville. The continuous lateral extent of Archaean SCLM precludes models for fossil subduction zones and sutures between domains or terranes within the presently outcropping Grenville Province. AMCG intrusions formed during both Labradorian rifting and collapse following 1.3 to 1.2 Ga Elzevirian crustal thickening of allochthonous terranes were emplaced between SCLM domains or along their margins. Fe-Ti mineralization in anorthosite and many other mineral occurrences in high-grade gneisses occur either above SCLM domain margins or above faults portrayed by the deep crustal satellite gravity component, commonly oblique to surface structures.

Several lithospheric scale structures identified are long lived, e.g. a WNW-ESE fault crossing the Superior Province continues beneath the Grenville, is offset by dextral shear zones that focused Neoproterozoic to Paleozoic rifting along the St Lawrence Estuary, and continues beneath the N Appalachians. This 'Waswanipi-Saguenay Corridor’ localised Archean, Paleoproterozoic, and Neoproterozoic carbonatite intrusions hosting Nb-Ta-REE mineralization and Paleozoic rifting which created the Saguenay Graben, which remains seismically active.

Research was funded by SOQUEM Québec.