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| Sturgeon Lake caldera | |
|---|---|
| Name | Sturgeon Lake caldera |
| Location | Ontario, Canada |
| Range | Canadian Shield |
| Type | Caldera |
| Last eruption | Archaean |
Sturgeon Lake caldera The Sturgeon Lake caldera is an ancient Archean volcanic structure in northwestern Ontario, Canada, situated within the Wabigoon Subprovince of the southern Superior Province. It preserves a package of felsic to mafic volcanic rocks and synvolcanic intrusions that record Archean magmatism contemporaneous with regional deformation episodes linked to the Kenora District greenstone belts, the development of the Canadian Shield, and continental assembly events recorded in the Superior craton. The complex is significant to studies of Archean tectonics, crustal growth, and Archean metallogeny, attracting investigations by academic institutions and geological surveys including the Geological Survey of Canada and the Ontario Geological Survey.
The Sturgeon Lake caldera occupies part of the volcanic stratigraphy in the Wabigoon Subprovince within the broader Superior Province of the Canadian Shield and lies near towns and infrastructures such as Dryden, Ontario, the Trans-Canada Highway corridor, and historic exploration camps tied to the Kenora District mining history. It forms one of several Archean volcanic centers that have been compared with other Archean calderas and greenstone-hosted systems such as those in the Huronian Supergroup, the Abitibi greenstone belt, and the Fort Frances area, and thus features in regional syntheses produced by the Mineral Exploration Research Centre and university research groups at institutions like the University of Toronto and Lakehead University.
The caldera developed during the late Archean, within a volcanic arc- to intra-arc setting interpreted from geological mapping, structural studies, and stratigraphic correlations by the Geological Survey of Canada and provincial geologists. Its formation involved eruption of high-silica rhyolites, intermediate and basaltic flows, and the emplacement of synvolcanic intrusive bodies; these assemblages are comparable to sequences described in the Swayze greenstone belt, the Michipicoten Greenstone Belt, and the Paarens Lake volcanic sequences. Regional deformation, metamorphism, and multiple phases of folding linked to tectonic events recognized in the Trans-Hudson Orogen and episodes recorded in the Superior Province modified original volcanic geometries, producing an arcuate structural basin interpreted as a collapsed roof typical of caldera-forming events.
Volcanic lithologies within the caldera include high-silica rhyolite flows and tuffs, dacitic units, and tholeiitic to calc-alkaline basalts, along with intrusive domes, sills, and dikes that host differentiated gabbroic to granitic compositions. These units show textures and alteration assemblages comparable to those reported from the Abitibi greenstone belt and the Chukotka Archean terranes, with pervasive hydrothermal alteration, silicification, and sulfide veining. Volcaniclastic sequences and pyroclastic facies preserve evidence for explosive eruptions comparable to sequences documented in the Wawa Subprovince and volcanic centers studied by researchers from the Royal Ontario Museum and the Ontario Geological Survey.
Geochronological constraints for the caldera derive from U–Pb zircon and baddeleyite dating, as well as from isotopic studies reported by teams at the Geological Survey of Canada and university laboratories; ages cluster in the late Archean, broadly coeval with magmatic events dated in the Wabigoon Subprovince and parts of the Berens River terrane. These absolute dates align the caldera with regional crustal growth pulses recorded across the Superior craton and with metamorphic and deformational timings constrained by thermobarometry and Ar–Ar studies undertaken by researchers at institutions such as McGill University and the University of Toronto.
The caldera is interpreted within a Archean tectonic framework involving arc-related magmatism, back-arc extension, and accretionary processes that assembled portions of the Superior Province. Interpretations draw on comparisons with convergent-margin models developed for the Abitibi greenstone belt, accretionary analogues considered for the Trans-Hudson Orogen, and structural syntheses prepared by the Ontario Geological Survey and the Geological Survey of Canada. Regional fault systems, shear zones, and synvolcanic grabens that traverse the area link the caldera to broader crustal strain patterns recorded across the Kenora District and the Wabigoon Subprovince.
The caldera and its host greenstone sequences are notable for polymetallic mineralization, including volcanogenic massive sulfide (VMS) style mineral deposits, gold-bearing quartz veins, and associated base-metal sulfide occurrences comparable to deposits in the Abitibi greenstone belt and the Midcontinent Rift exposures. Prospecting and resource assessments by the Ontario Geological Survey, junior exploration companies, and academic studies have documented occurrences of pyrite, chalcopyrite, sphalerite, and native gold hosted in alteration zones, felsic domes, and shear-hosted veins. These targets have drawn interest from exploration firms listed on exchanges such as the Toronto Stock Exchange and the TSX Venture Exchange, and have been the focus of geochemical, geophysical, and drilling campaigns.
Research on the caldera has progressed from early regional mapping by the Geological Survey of Canada and provincial field parties to detailed petrological, geochemical, and geochronological investigations by university groups, government surveys, and industry-led exploration programs. Key contributions include mapping campaigns by the Ontario Geological Survey, zircon U–Pb studies by laboratories associated with University of Waterloo and McGill University, geophysical surveys funded through provincial initiatives, and integrated syntheses produced in collaboration with the Mineral Exploration Research Centre. Ongoing work continues to refine models for Archean caldera dynamics, volcanogenic mineralization, and crustal evolution across the Superior craton.
Category:Volcanic calderas of Ontario Category:Archean geology