Dating shear zones with plastically deformed titanite: New insights into the orogenic evolution of the Sudbury impact structure (Ontario, Canada)

Abstract

The Sudbury structure is a mineralized impact crater that hosts different families of ore-controlling shear zones with poorly known orogenic affinities. Discriminating whether these deformation events relate to the 1.85Ga crater modification stage or later regional tectonism, that collapsed the impact structure, is important both for crustal and mineral exploration studies. We have combined underground mapping with isotopic and microstructural analysis of titanite and host minerals in a benchmark ore-controlling mylonitic shear zone of the mining camp, the Six Shaft Shear Zone from the Creighton Mine. Three growth stages of chemically and microstructurally-characterised titanite grains were identified related with the pre-, syn and late deformation stages. In-situ U-Pb age dating of the syndeformational grains demonstrates that a shearing event took place at 1645±54Ma during the Mazatzalian–Labradorian orogeny (1.7–1.6Ga). This event led to the plastic deformation and local-scale remobilization of primary Ni-Cu-PGE sulphides in Creighton Mine (Sudbury, South Range). The adopted novel petrochronological approach can reveal the age significance of syn-deformational processes and holds promise for the untangling of complex syn-orogenic processes in Precambrian terranes globally.