Possible causes and consequences of regional Na-metasomatism: the case of the Sudbury Impact Structure, Ontario, Canada

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Sodium metasomatism is a widespread geological phenomenon on a regional scale over distances of hundreds of kilometers, the causes of which, especially within the continental crust, are poorly understood so far. It can be related to pervasive circulation of NaCl-rich solutions derived from metamorphism of evaporitic, halite-bearing sedimentary sequences, or to possibly magma-derived overpressured fluids that can have a high mineralizing potential as exemplified by iron oxide-copper-gold (IOCG) deposits. One of the most obvious mineralogical expressions of Na-metasomatism is albitization, an extreme metasomatic process that results in the mobility even of elements traditionally considered relatively fluid-immobile. Regional albitization of Palaeoproterozoic rocks is a well-known but poorly understood phenomenon in the area around the 1.85 Ga Sudbury impact structure (one of the biggest of its kind in the world) in Ontario (Canada). Based on results achieved in a recent DFG-supported project in the area, it is more widespread than previously recognized and intimately associated with intense brecciation. Its age and geological cause remain unresolved. Albitization and brecciation could be related to the Sudbury impact but also to sodic alkali magmatism or basin-wide fluid circulation in the course of Palaeoproterozoic orogenies. The aim of this research project is the characterization of the type and extent of Na-metasomatism in the area around Sudbury and to clarify whether it is related to the impact event, to alkaline magmatism unrelated to the impact or to some other cause altogether. In the former case, it would have consequences on our understanding of how hydrothermal systems could be formed by impacts on the (early) Earth surface with implications on the formation of early life environments. In the case of a non-impactogenic but magmatogenic origin, however, it would have profound implications for the prospectivity of the region for a range of commodities, including critical metals, as typically found in IOCG ore districts or alkaline magmatic provinces. The said aim will be achieved through a combination of geological field work, petrography, mineralogical, mineral-chemical, geochemical and isotopic studies as well as geochronological analyses.