Emplacement of the Foy, Hess and Pele Offset Dykes at the Sudbury impact structure, Canada

Author

Eric A. Pilles, The University of Western OntarioFollow

Degree

Doctor of Philosophy

Program

Geology

Supervisor

Gordon Osinski

Abstract

The 1.85 Ga Sudbury impact structure is the remnant of what is generally considered to have been an ~150–200 km diameter impact basin in central Ontario, Canada. The so-called Offset Dykes are impact melt dykes that are found concentrically around – and extending radially outward from – the Sudbury Igneous Complex (SIC), a ~3 km thick differentiated impact melt sheet. The dykes are typically composed of two main phases of granodiorite: an inclusion- and sulfide-rich granodiorite in the centre of the dyke, and an inclusion- and sulfide-poor granodiorite along the margins of the dyke. This study uses a combination of field mapping, petrography, electron microprobe analyses and geochemical data to address two outstanding questions regarding the temporal relationships of the Offset Dykes: (1) When were the Offset Dykes emplaced relative to the impact cratering process and differentiation of the SIC and; (2) What is the relationship between the internal phases of the Offset Dykes (i.e., inclusion-rich and inclusion-poor granodiorite). New exposures of the Foy and Hess Offset dykes, along with the recent discovery of the Pele Offset Dyke, provide an excellent opportunity to understand the relationship between the Offset Dykes in the North Range of the SIC. From this research, a number of conclusions can be drawn: (1) The Foy and Hess were intruded after the SIC had undergone some degree of differentiation; (2) The Hess is slightly less evolved than the Foy with respect to the SIC, but the two dykes co-existed as melts and mixed at the intersection; (3) The Foy was likely emplaced during a single prolonged event, which carried the clasts and sulfides, and subsequent flow differentiation moved the clasts and sulfides towards the centre of the dyke, forming the inclusion-poor and inclusion-rich phases and; (4) The Pele is composed of only the inclusion-poor phase, is chemically more evolved than the other North Range Offset Dykes, and may have been one of the last Offset Dykes to have been emplaced. These results suggest that emplacement of the Offset Dykes took place over an extended period of time and not as a single early injection event.

Recommended Citation

Pilles, Eric A., "Emplacement of the Foy, Hess and Pele Offset Dykes at the Sudbury impact structure, Canada" (2016). Electronic Thesis and Dissertation Repository. 4158.
https://ir.lib.uwo.ca/etd/4158