Geochemical Variation Along Strike of the Hess Offset Dyke at the Sudbury Impact Structure, Canada

English Abstract:

The Sudbury Impact Structure is a 1.85Ga impact structure located on the contact between the Superior Province Archean granite-greenstone terrain to the North and the Southern Province Huronian Supergroup to the south. The Offset Dykes extend radially outward from – and concentrically around – the Sudbury Igneous Complex (SIC), which is a ~3-km thick differentiated impact melt sheet. The Hess is the longest of the concentric Offset Dykes, with a strike length of ~60 km. It is located ~12–15km northwest from the SIC, hosted in the Superior Province. The Hess is up to 60m wide and is composed of two phases: an inclusion-poor granodiorite along the margins of the dike and an inclusion-bearing granodiorite in the centre of the dike.

There is very little difference in major element geochemistry when comparing the two phases, and only minor variations in trace elements. However, the matrix of the inclusion-bearing phase is notably enriched in light REEs compared to the inclusion-poor phase. This observed variation is minimal compared to the differences found along strike of the Hess – from the westernmost end in the Ermatinger Township to the northernmost end where the Hess intersects the Foy.

The samples closer to the west end of the dyke were more depleted in Si, K, Li, Ba, and light REEs; and more enriched in Ti, Fe, Mn, Mg, Sc, and V compared to the samples located near the Foy-Hess intersection. The samples located near the middle of the dyke show anomalous variation as well. At some locations they are more consistent with results from the west end samples, and at others they are more consistent with results from samples near the intersection. The reason(s) for these geographical variations in composition are currently being explored.