Deep Into the Chibougamau Area, Abitibi Greenstone Belt: Structure of a Neoarchean Crust Revealed by Seismic Reflection Profiling

Abstract

Copper‐gold 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., a possible deep continuation of the Barlow fault) and a northward‐dipping midcrust imbricated with older crust (Opatica subprovince) to the north. Multiple reflectors characterize the upper part of the midcrust, 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.

Oxygen Fugacity and Volatile Content of Syntectonic Magmatism in the Neoarchean Abitibi Greenstone Belt, Superior Province, Canada

“…For that reason, this study focuses on the Chibougamau area, where a variety of syntectonic magma types (sanukitoid, alkaline intrusions, granitoid) are observed, and gold deposits are not overprinted by features characteristic of orogenic gold systems-a mineralizing style that is not abundant in the study area. Furthermore, magmatic-hydrothermal systems are unusually abundant in the Chibougamau area (e.g., central camp, MOP-II, Lac Line mineralization) [10][11][12], although the tectonic processes causing this remain unclear [13,14]. The abundance of such mineralizing systems in this area offers a unique opportunity to study the chemistry of 'fertile' magma intrusions.…”

Multidisciplinary Modeling of Mantle Lithosphere Structure Within the Superior Craton, North America

“…Dipping seismic reflectors observed on Lithoprobe and on more recent deep seismic reflection sections mark where the mafic crust was underthrust, in a general north to south sequence (Figure 2) (Calvert et al, 1995;Mathieu et al, 2020;White et al, 2003). Contrasting models suggest either serial subduction SNYDER ET AL.…”

“…Dipping seismic reflectors observed on Lithoprobe and on more recent deep seismic reflection sections mark where the mafic crust was underthrust, in a general north to south sequence (Figure 2) (Calvert et al., 1995; Mathieu et al., 2020; White et al., 2003). Contrasting models suggest either serial subduction zones (Percival et al., 2006), or subcretion to the leading edge of a drifting proto‐craton (Bédard & Harris, 2014), or progressive rifting (Bjorkman, 2017; Mints, 2017).…”

“…Higher‐resolution seismic sections near Timmins in the Abitibi terrane further revealed numerous symmetric upright folds in the upper and mid‐crust, in places stacked and thus steepened (Snyder et al., 2008). In contrast, Metal Earth seismic reflection sections from throughout the southern Superior craton (Figure 1) show near‐horizontal sets of sub‐parallel reflectors in the upper to mid‐crust that are laterally continuous for 10–20 km (Mathieu et al., 2020; Naghizadeh et al., 2019). Breaks in these continuous reflectors align roughly vertically to form disrupted zones up to several kilometers wide, typically beneath surface rocks with near‐vertical dips, in places associated with shear zones.…”

Intrusion-Associated Gold Systems and Multistage Metallogenic Processes in the Neoarchean Abitibi Greenstone Belt

“…(3) cratonization, including a succession of sedimentation and deformation events. An example of such evolution is proposed for the Chibougamau area, northeastern corner of the Abitibi greenstone belt [7]. The main geodynamic processes characterizing the construction, maturation, and cratonization stages are topics of considerable debate, as reviewed recently [8].…”