\sout\sout Copper-Au magmatic-hydrothermal systems dominate in the Chibougamau area of the Neoarchean Abitibi Subprovince, whereas orogenic gold mineralization is more common in the rest of the Abitibi. Understanding differences in the metal endowment of parts of the Abitibi Subprovince requires insights into the geodynamic evolution of the Chibougamau area. This is addressed by imaging the crust using seismic reflection data acquired as part of the Metal Earth project. Seismic reflection imaged shallowly south-dipping structures in the upper-crust (e.g., deep extension of the Barlow fault) and a northward-dipping mid-crust region. The upper part of the mid-crust zone is characterized by multiple reflectors that are likely faults superimposed on a major lithological boundary. These structures were likely acquired at ca 2.70 Ga during terrane accretion prior to carbonization. Combining the seismic data with known stratigraphic, structural and magmatic records, we propose that the study area was initially a normal (i.e., thick) Archean oceanic crust that formed at or before 2.9 Ga and that evolved through terrane imbrication at 2.73 Ga or before. This caused rapid burial of mafic rocks followed by devolatilization and partial melting of hydrated mafic rocks to produce tonalite magmas that may have mixed with mantle-derived melts to produce the diorite-tonalite suite associated with Cu-Au magmatic-hydrothermal mineralization.

Copper-Au magmatic-hydrothermal systems dominate in the Chibougamau area of the Neoarchean Abitibi subprovince (greenstone belt) of the Superior Province (craton), whereas orogenic gold mineralization is more common in the rest of the Abitibi. Understanding differences in metal endowment within the Abitibi greenstone belt requires insights into the geodynamic evolution of the Chibougamau area. This was addressed by imaging the crust using seismic reflection profiling acquired as part of the Metal Earth project. Seismic reflection sections display shallowly south-dipping reflectors located within the upper-crust (e.g., deep continuation of the Barlow fault) and a northward-dipping mid-crust imbricated with older crust (Opatica subprovince) to the north. Multiple reflectors characterize the upper part of the mid-crust, interpreted as faults superimposed on a major lithological boundary. These structures likely formed during terrane accretion prior to craton stabilization. Combining the new seismic data with known stratigraphic, structural and magmatic records, we propose that the study area was initially a normal (i.e., thick) Archean oceanic crust that formed at or before 2.80 Ga and that evolved through terrane imbrication at 2.73-2.70 Ga. Shortening caused rapid burial, devolatilization and partial melting of hydrated mafic rocks to produce tonalite magmas that may have mixed with mantle-derived melts to produce the diorite-tonalite suite associated with observed Cu-Au magmatic-hydrothermal mineralization.