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: (i) All other known Offset Dykes consist of an inclusion-rich lithology in the center of the dyke and an inclusion-poor lithology along the margins. The Pele dykes, however, are only composed of the inclusion-poor phase. (ii) 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.

Modeling the geochemical evolution of impact melts in terrestrial impact basins: Vredefort granophyre dikes and Sudbury offset dikes

“…B) Classification of rocks based on trace element composition after Winchester and Floyd (1977). Offset dikes data from Pilles et al (2017), Hecht et al (2008), Lightfoot et al (1997a), and Tuchscherer and Spray (2002). (Color figure can be viewed at wileyonlinelibrary.com.…”

“…We have juxtaposed the results from the Vredefort granophyre with those from the Pele (Pilles et al. 2017), Foy (Tuchscherer and Spray 2002; Pilles et al. 2017), Hess (Pilles et al.…”

“…2C; Hecht et al 2008). A recent description of the offset dikes can be found in Pilles et al (2017).…”

“…Despite forming at different geological times and on different cratons, the Vredefort granophyre dikes appear to have developed through equivalent geochemical evolutionary trends to the Sudbury offset dikes . We have juxtaposed the results from the Vredefort granophyre with those from the Pele (Pilles et al 2017), Foy (Tuchscherer and Spray 2002;Pilles et al 2017), Hess (Pilles et al 2017), and Worthington (Hecht et al 2008) offset dikes. The bulk composition of the SIC is plotting in the center of the compositional range of the offset dikes and Vredefort granophyre (Fig.…”

“…For the purposes of modeling, only major elements were considered (SiO 2 , TiO 2 , Al 2 O 3 , FeO, MgO, CaO, Na 2 O, K 2 O, P 2 O 5 ). The initial liquid compositions tested were the bulk composition of (a) the upper continental crust (UCC) estimation of Wedepohl (1995), as this is based on estimates from the Canadian Shield, which should be most relevant for the Sudbury impact structure; (b) the Archean UCC as given by Condie (1993), as this was the target for Vredefort; (c) the SIC (Kring 1995), as this is a reasonable starting melt composition for both melt sheets; and (d) the SIC norite (Pilles et al 2017), as the lower, mafic portion of the melt sheet has previously been suggested as a source for Fig. 6.…”