Chemical variations and genetic relationships between the Hess and Foy offset dikes at the Sudbury impact structure

Abstract

Offset dikes are found concentrically around—and extending radially outward from—the Sudbury Igneous Complex (SIC), which represents an ~3 km thick differentiated impact melt sheet. The dikes are typically composed of an inclusion‐rich, so‐called quartz diorite (IQD) in the center of the dike, and an inclusion‐poor quartz diorite (QD) along the margins of the dike. New exposures of the intersection between the concentric Hess and radial Foy offset dikes provide an excellent opportunity to understand the relationship between the radial and concentric offset dikes and their internal phases. The goal was to constrain the timing of the dike emplacements relative to the impact and formation of the SIC. Results herein suggest that (1) the timing between the emplacement of the QD and IQD melts was geologically short, (2) the Hess and Foy dikes coexisted as melts at the same time and the intersection between them represents a mixture of the two, (3) the Foy dike has a slightly more evolved chemical composition than the Hess dike, and (4) the IQD melt from the Foy dike underwent some degree of chemical fractionation after its initial emplacement.

The Pele Offset Dykes, Sudbury impact structure, Canada

“…Dyke, and the Granophyre and Norite units of the SIC. The data from the Foy (Pilles et al 2017) and the SIC (Therriault et al, 2002) are depicted as ellipses, which represents the p = 0.95…”

Structural controls on the localization of the mineralized Copper Cliff embayment and the Copper Cliff Offset dyke, Sudbury Igneous Complex, Canada

“…The CCO is an approximately N-S-striking dyke, the thickness of which decreases southward from 100 to 3 m. The southernmost part of the dyke cooled more rapidly, as indicated by the thicker quenched margins (Grant and Bite, 1984 ), and the QD/IQD ratio increases southward (Table 4). The IQD-QD contact is a melt-melt contact, indicating a protracted emplacement of QD and IQD phases, as observed in other Offset dykes (Lightfoot, 2017;Pilles et al, 2017). The table layout displayed in this section is not how it will appear in the final version.…”