New U-Pb geochronological constraints on the tectono-magmatic evolution of the Chibougamau-Chapais region, northeastern Abitibi greenstone belt, Québec

The tectonomagmatic evolution of the Chibougamau-Chapais area, a peripheral part of the Abitibi belt, is revealed using compiled and new high-resolution geochronological data. Results indicate that volcanism, as old as 2803 Ma and best documented in the 2730 – 2714 Ma time interval, was dominantly tholeiitic and mafic at first, and progressively became more felsic and calc-alkaline. Melts extracted from mantle and mafic crustal sources formed coeval magmatic systems that hybridized locally to produce diorite. Most large volume tonalite and diorite intrusions assembled at ca. 2720 – 2714 Ma, as a sagging central volcano got established in the northern half of the Chibougamau-Chapais area and induced deformation (possibly uplift and erosion) in the basalt-dominated southern half of the area. Felsic magmatism then migrated to the south, producing the youngest volcanic unit (ca. 2715 Ma Phooey Member) and tonalite intrusion (ca. 2712 Ma Hazeur pluton) of the area prior to compressional deformation at ca. 2712 – 2710 Ma. The subsequent time interval is characterized by extension, basin-restricted sedimentation, and by medium to large volume K-enriched magmatism in the upper crust, with magma production peaking at 2697 – 2695 Ma prior to the main regional N-S shortening event. This is followed by localized extension (stress relaxation) in the central part of the study area and along a WNW-ESE corridor defined by ca. 2688 – 2685 Ma alkaline magmatism.