Deep into the Chibougamau area, Abitibi greenstone belt: structure of a
Neoarchean crust revealed by seismic reflection profiling
Abstract
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.