Tectonic models for the origin of regional transverse structures in the Grenville Province of SW Quebec interpreted from regional gravity

Abstract

Analysis of regional gravity data over the Grenville Province of SW Québec, Canada, has identified hitherto unrecognized transverse deep-crustal structures, in addition to lineaments that correspond to mapped upper crustal, orogen-parallel tectonic boundaries. Lineaments that trend NW–SE, i.e. transverse to the orogen, are interpreted as reactivated Palaeoproterozoic faults in Archaean basement that are controlled by structures in Archaean sub-crustal lithospheric mantle (SCLM). A prominent lineament (the Mont-Laurier lineament) that extends from the SE Superior Province across the SW Grenville Province is identified on both gravity and seismic tomographic imagery, the latter confirming it represents a lithospheric-scale structure. Baltica is placed at the Laurentian margin in tectonic reconstructions, and the Mont-Laurier lineament correlates with the extension towards the Superior Craton of the Belomorian Province between the Karelia and Kola cratons. It is proposed that this structure developed as a normal fault zone, and was subsequently reactivated as a transfer fault, during two orthogonal Palaeoproterozoic rifting events. The ensuing irregular basement geometry subsequently influenced sedimentation and deformation during the Grenvillian orogenic cycle and the Mont-Laurier lineament again acted as a transfer fault zone during Grenvillian orogenesis and post-orogenic collapse. Identification of tranverse structures has implications in understanding the architecture of this part of the Grenville Province. The role of pre-existing basement structures and rigid SCLM on the formation and preservation of long, linear structures transverse to an orogen throughout a complex sequence of rifting, back-arc basin formation, collisional orogenesis, and post-orogenic collapse in the Grenville Province of SW Quebec is also documented in New Guinea, with which comparisons are made.