The Pele Offset Dykes, Sudbury impact structure, Canada

Abstract

The Offset Dykes are impact-melt bearing dykes related to the 1.85 Ga Sudbury impact structure. Currently, the dykes extend radially outward from – or occur concentrically around – the Sudbury Igneous Complex, which is the remnant of a differentiated impact melt sheet and the source of the dykes. The recently identified three Pele Offset Dykes intrude into the Archean rocks north of the Sudbury Igneous Complex. In this study, the Pele dykes are characterized for the first time by a combination of fieldwork, optical microscopy, electron microprobe analyses, and bulk geochemical analyses. The Pele Offset Dykes stand out from the other Offset Dykes at Sudbury in two significant ways: (1) All other known Offset Dykes consist of an inclusion-rich lithology in the centre of the dyke and an inclusion-poor lithology along the margins. The Pele dykes, however, are only composed of the inclusion-poor phase. (2) The Pele dykes – particularly the Central and Eastern dykes – have a more evolved chemical composition relative to the other Offset Dykes. These observations suggest that the Pele dykes were emplaced after the other known Offset Dykes during two injection events: the Western followed by the Central and Eastern Pele dykes.