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

Abstract

[1] 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.

Using Trace Elements in Chromites to Constrain the Origin of Podiform Chromitites in the Thetford Mines Ophiolite, Quebec, Canada

“…1A), which represents remnants of the Iapetus Ocean and its marginal basins (the Dunnage zone: Williams and St-Julien, 1982;Hébert and Laurent, 1989;Laurent and Hébert, 1989) obducted onto the Laurentian margin (the Humber zone) during the Taconic orogeny (Fig. 1A;St-Julien and Hubert, 1975;Williams and St-Julien, 1982;Schroetter et al, 2005). The newly accreted oceanic terranes have been reworked by two postemplacement tectonic events: the Upper Silurian-Lower Devonian Salinic tectonic episode and the Middle Devonian Acadian orogeny, a major contractional event resulting from the final closure of the Iapetus Ocean (Osberg, 1978;Williams and Hatcher, 1983;Robinson et al, 1998;van Staal et al, 1998;Tremblay and Castonguay, 2002).…”

Shallow, old, and hydrologically insignificant fault zones in the Appalachian orogen

“…Four tectonostratigraphic zones are recognized in southern Quebec, from northwest to southeast: the (1) Grenville Province, (2) the St. Lawrence platform, (3) Appalachian foreland basin (autochthonous domain), a fault-imbricated zone (parautochthonous domain), and (4) the Appalachian thrust sheets (allochthonous domain) [De Souza and Tremblay, 2010;Sasseville et al, 2008;Schoonmaker and Kidd, 2007;Schroetter et al, 2005Schroetter et al, , 2006Séjourné et al, 2003;Séjourné and Malo, 2007;Séjourné et al, 2005]. The southern and northern study areas are located in the Appalachian thrust sheets ( Figure 2) which are generally divided into the Cambrian-Ordovician Humber and Dunnage Zones [Schroetter et al, 2006;Williams, 1979].…”

“…The faults are primarily thrust faults, including some back thrusts [Schroetter et al, 2005[Schroetter et al, , 2006. Fault deformation occurred before, during, and after the Ordovician Taconian orogeny, during the Late Silurian to early Devonian and during the Devonian Acadian orogeny [Sasseville et al, 2008;Séjourné and Malo, 2007].…”

The Vardar zone as a suture for the Mirdita ophiolites, Albania: Constraints from the structural analysis of the Korabi-Pelagonia zone

“…From a structural point of view, the obduction of Tethyan‐type ophiolites includes the following events, from the oldest to the youngest [e.g., Wakabayashi and Dilek , ]: (1) intraoceanic subduction and formation of a suprasubduction zone (SSZ) ophiolite and its infraophiolitic metamorphic sole, (2) exhumation of the metamorphic sole relative to the ophiolite, (3) foreland propagating, piggyback style of thrusting of the ophiolite and its metamorphic sole over the continental margin, and (4) subaerial exposure of both the ophiolite and underlying metamorphic rocks. In principle, the structural polarity of obducted ophiolites should be thus recorded in their metamorphic soles and underlying low‐grade sedimentary rocks [ Searle et al ., ; Wakabayashi and Dilek , ; Schroetter et al ., ; Tremblay et al ., ]. In Albania, the structural and microstructural analysis of the sole rocks of the Mirdita ophiolites unfortunately yields contradictory results, showing both west‐over‐east and east‐over‐west shear‐sense indicators [ Collaku et al ., ; Dimo‐Lahitte et al ., ].…”