Abstract

Fifty-seven samples of the Turriff metavolcanic sequence from the Hastings region of the Grenville Province have been chemically analyzed. Ten major-element oxides and ten trace-element values for each sample were determined by standard X-ray fluorescence techniques. The sampled sections consist predominantly of mafic flows, subordinate intermediate flows, and minor felsic flows and pyroclastics. The sequence has been regionally metamorphosed to lower amphibolite facies. The geochemical data indicate that the metavolcanics represent a tholeiitic mafic–silicic bimodal sequence. Immobile-element discriminant diagrams indicate that the Turriff metabasalts are most similar to recent oceanic ridge basalts, whereas the metabasalts from other published studies of Grenville metavolcanics have an island-arc tholeiite affinity. However, because of the many chemical similarities between continental and oceanic ridge tholeiites, the bimodal nature of the sequence, and the field relationships, it is most likely that the eruption of the Turriff metavolcanics was associated with the rifting of continental crust, perhaps leading to the development of a marginal sea.

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