Age and Geochemical Character of Granite and Syenite Plutons in the Grenville Province of Southeastern Ontario; Insights into Magmatism During the Ottawan Orogeny and Evidence of the Frontenac Intrusive Suite in the Sharbot Lake Domain

Abstract

Seven plutons in the Composite Arc Belt and Frontenac terrane of the Grenville Province are herein determined to be part of the Kensington-Skootamatta intrusive suite. The syenite-monzonite and granite-monzogranite plutons have crystallization ages of ca. 1086-1072 Ma and ca. 1077-1067 Ma, respectively. In general, the plutons are shoshonitic, metaluminous to weakly peraluminous, and alkalic to calc-alkalic. The plutons have conflicting trace element signatures that suggest a within-plate tectonic setting with a weak remnant suprasubduction zone signature and a depleted mantle isotopic signature of eNd 2-5. This geochemistry points to derivation of these melts through fractionation of an alkaline basalt or partial melting of quartzofeldspathic crust. Melt generation was perhaps initiated by crustal delamination, and further heated through insulation by overthickened crust and the Midcontinent Rift magmatic system. Two other plutons that were studied have ca. 1180-1160 Ma crystallization ages and geochemical characteristics similar to the Frontenac intrusive suite.