Petrogenesis of Cambro-Ordovician subduction-related granitic magmas of the Québec Appalachians, Canada

In the Québec Appalachians, Cambro-Ordovician subduction-related granitic rocks are found as intrusive bodies (ACI) in the Ascot Complex volcanic arc and as eroded fragments (MGC) in the adjacent Magog Group sedimentary basin. Major- and trace-element geochemistry indicates that ACI and MGC rocks are typical peraluminous granitoids. Both suites are LREE-enriched with minor negative Eu anomalies; ACI granitoids displaying higher MREE and HREE abundances than MGC. REE and trace-element data indicate that ACI and MGC granitoids are chemically similar, but differences in their respective fractionation trends and trace-element ratios demonstrate a significant petrological decoupling. 143Nd144Nd are higher in the MGC granitoids than in the ACI. Both suites display negative ϵNd ratios (−10 to −3) implying limited juvenile material input. Sm-Nd isotopes from both suites suggest that they originated from the anatectic partial melting of a compositionally-zoned, Grenville-like continental crust.