Structural evolution of the Thetford Mines Ophiolite Complex, Canada: Implications for the southern Québec ophiolitic belt

Abstract

The Thetford Mines Ophiolite Complex (TMOC) preserves a complete ophiolitic sequence, and occupies the hanging wall of a major SE dipping normal fault, the Saint‐Joseph fault. Preobduction, synobduction, and postobduction structures can be recognized in the TMOC. NS trending, preobduction, paleonormal faults are parallel to ultramafic minor intrusions, and to sheeted dykes, recording extension related to seafloor‐spreading in a pericontinental suprasubduction zone basin. WNW trending synobduction, synmetamorphic fabrics are found toward the base of the TMOC and in the underlying continental margin rocks, but are absent in the upper part of the TMOC and overlying sedimentary rocks. These Ordovician (Taconian) structures record the development of a dynamothermal aureole immediately below the mantle/margin contact, and emplacement of the young ophiolite onto the continental margin. Postobduction structures include Late Silurian/Early Devonian, SE verging backthrusts and back folds that inverted the TMOC; and Middle Devonian (Acadian) NW verging folds and reverse faults. The tectonic history established for the TMOC is consistent with that of the adjacent Laurentian margin, and can be applied to the southern Québec ophiolitic belt as a whole. The structural synthesis of the ophiolitic belt, complemented with new observations and our compilation of stratigraphical, geochemical, geochronological, and petrological data, suggests that the southern Québec ophiolites may represent the remnants of the obduction of a single large slab of suprasubduction oceanic lithosphere extending for over a 100 km of strike length.