Fried Schwerdtner (Emeritus)
University of Toronto Department of Earth Sciences
22 Russell Str. Toronto Ontario, Canada M5S 3B1
Tel.: 416 978 5080 Fax.: 416 978 3938
Late-orogenic cross-folds in the Ottawa River Gneiss Complex, western Grenville Province: Shear-induced sheath folds or products of superimposed deformation?
Field-based litho-structural study of the Ottawa River gneiss complex (Ontario portion), relict lower plate of a continental metamorphic core complex, southwest Grenville Province, southeast Canadian Shield
Continental metamorphic core complexes (MCCs) consist of (1) an exhumed, mid-crustal, antiformal gneissic core, also known as the ‘lower plate’, (2) an extensional dislocation at the top of the core, also known as the ‘detachment’, and (3) an overlying ‘upper plate’ comprising the extended, low metamorphic grade cover. In some MCCs, the detachment is represented by two conjugate outward-dipping, spatially-unconnected, extensional shear zones. A well-studied example are the conjugate Columbia River and Okanagan Valley shear zones in the southern Canadian Cordillera, which detach the early-Tertiary Shuswap Complex (lower plate) from its low metamorphic grade cover (upper plate).
The Proterozoic Grenville Province of the Canadian Shield, a 2000-km-long segment of an ancient collisional orogen, is interpretable as a NE-SW chain of large MCCs (Rivers 2012, Can. J. Earth Sci., 49: 1-42, his Figs. 2, 14). Since 2011, Rivers, Schwerdtner and their coworkers have investigated the Ontario portion of the westernmost Grenvillian MCC (see references listed below). The gneissic core/lower plate of this MCC, the Ottawa River gneiss complex (ORGC, see sketch map below), consists of repeatedly deformed, parautochthonous and allochthonous high-grade metamorphic rocks with Nd model ages ranging from Archean to Mesoproterozoic (Dickin 2000, Can. J. Earth Sci., 37: 165-181). At the SE flank, the ORGC was detached from the overlying upper plate, a portion of the disrupted Ottawan Orogenic Lid (Rivers 2012, op. cit.), by extensional reactivation of a 1090–1960 Ma reverse-sense shear zone, known as the Composite Arc Belt boundary zone. In contrast, the NW flank of the ORGC was reworked and subjected to superimposed ductile deformation at ca. 1000 Ma during formation of the SE-dipping Grenville Front and Grenville Front Tectonic Zone. Therefore, the original width of the ORGC, its detachment mode and the dip direction of its original NW contact are difficult to determine.
In 2019-20, the ongoing collaborative research will focus special attention on the post-convergent litho-structural evolution of the Algonquin domain (Burk’s Falls, Dwight and Huntsville regions). In addition, the mesoscopic structure of the ORGC detachment (SE flank), better known as the Composite Arc Belt boundary zone, will be re-examined in blasted road cuts and other clean rock exposures of the Carnarvon and Minden areas. Specific mesoscopic structural data will be collected to permit the use of published numerical models that simulate the evolution of tight to isoclinal asymmetrical folds.
Left: Southeast-dipping granitoid gneiss, Hwy. 60 north of Smoke Lake, southwest Algonquin Park, ON.
Centre: Relict S-Z structure, Hwy. 11 near Emsdale ON.
Right: Relict S-Z structure, Hwy. 520, between Burk’s Falls and Lake Cecebe, ON.
Schwerdtner, W.M., Rivers, T., Tsolas, J., Waddington, D.H., Page, S., and Jang, J. 2016. Transtensional origin of multi-order cross-folds in a high-grade gneiss complex, south- western Grenville Province: formation during postpeak gravitational collapse. Canadian Journal of Earth Sciences, 53: 1511-1538.
Rivers, T. and Schwerdtner, W.M. 2015. Post-peak evolution of the Muskoka Domain, western Grenville Province: ductile detachment zone in a crustal-scale metamorphic core complex. Geoscience Canada, 42: 403-436.
Schwerdtner, W.M.,Rivers, T., Zeeman, B., Wang, C.C., Tsolas, J., Yang, J., and Ahmed, M. 2014. Post-convergent structures in lower parts of the 1090-1050 Ma (early Ottawan) thrust-sheet stack, Grenville Province of Ontario, southern Canadian Shield. Canadian Journal of Earth Sciences, 51 243-265
Schwerdtner, W.M. 2013. Photograph of the month. Journal of Structural Geology, 48 (October issue): 1-2.
Schwerdtner, W.M. and Yang, J.F. 2011. Photograph of the Month: Pseudotachylite at the basal contact of the Parry Sound allochthon, Grenville Province of Ontario, Canada. Journal of Structural Geology, 33: 1714.
Schwerdtner, W.M., Lu, S. J. and Yang, J.F., 2010. Wall-rock structure at the present contact surfaces between repeatedly deformed thrust sheets, Grenville Orogen of central Ontario, Canada. Canadian Journal of Earth Sciences, 47: 875-899.
Schwerdtner, W.M., Lu, S.J. and Landa, D., 2010. S/Z buckle folds as shear-sense indicators in the ductile realm: Field examples from the Grenville Province of Ontario and the Appalachians of South Carolina. In ‘From Rodinia to Pangea: The Litho- tectonic record of the Applachian Region, Geological Society of America Memoir 206, Chapter 30, p. 773-794.
Schwerdtner, W.M. and Klemens, W.P., 2008. Structure of the Ahmic domain and its vicinity, southwestern Central Gneiss Belt, Grenville Province of Ontario (Canada). Precambrian Research, 167: 16 – 34.
Schwerdtner, W.M., Riller, U.P. and Borowik, A., 2005. Structural testing of tectonic hypotheses by field-based analysis of distributed tangential shear: examples from major high-strain zones in the Grenville Province and other parts of the Canadian Shield. Canadian Journal of Earth Sciences, 42: 1927 – 1947.
Schwerdtner, W.M., Downey, M.W. and Alexander, S.A., 2004. L-S shape fabrics in the Mazinaw domain and the issue of NW-directed thrusting in the Composite Arc Belt, southeastern Ontario. Geological Society of America, Memoir 197, p. 183 – 2008.
Rivers, T. and Schwerdtner, W.M. 2014. New ideas on the post-peak development of the Central Gneiss Belt in the Muskoka Region. Field trip guide, Friends of the Grenville weekend in Gravenhurst, Ontario; October 3-5, 2014.
Schwerdtner, W.M., Robin, P.-Y. F., Alexander, S., Burke, J., Downey, M.W., and Serafini, G., 2003. Connection between Grenvillian deformation and granitoid pluton emplacement in the Composite arc Belt (Tweed-Kaladar area), southestern Ontario, Canada. Guidebook for Friends of the Grenville (Amis du Grenville) field trip, Department of Geology, University of Toronto.
Schwerdtner, W.M., Klemens, W.P., Robin, P.-Y. F., Vertolli. V.M., and Waddington, D.H., 2005. Geological structure and lithology in parts of the Muskoka region, southwestern Central Gneiss Belt, Grenville Province of Ontario. Field trip guide, 25th annual workshop of the Canadian Tectonics Group and Structural Geology-Tectonics Division of the Geological Association of Canada, Department of Geology, University of Toronto.
Schwerdtner, W.M., Dickin, A.P. and Robin, P.-Y. F., 2009. Rocks, structures and tectonic scenarios: Introduction to the Grenville Province of Ontario. Guidebook for a pre-sessions field trip (Geological Association of Canada), Joint Assembly (AGU- GAC-MAC Meeting), Department of Geology, University of Toronto.