The relative roles of ancient and juvenile crust in building accretionary orogens-Minimal ancient crust involved in the magmatic evolution of a North American Cordillera accreted terrane indicated by igneous zircon Hf-O

New igneous zircon Hf-O data from the Hogem batholith (207 to 125 Ma), emplaced into the Quesnel arc, an accreted oceanic terrane in the northern Cordillera, resolve questions about the magmatic history and source inputs of the terrane and the relationship of the terrane with ancestral North America before, during, and after collision. Juvenile zircon Hf signatures (> + 5 initial & epsilon;Hf) with predominantly mantle-like 818O (+5.3 & PLUSMN; 0.6%o) indicate juvenile, mantle-derived magmas as the major contributors to the Hogem batholith. Minor input from young recycled oceanic crust is indicated by less common heavy zircon 818O (>6.5%o). Mixing models demonstrate that ancestral North American crust did not underlie or contribute to the construction of north-central Quesnellia during the Triassic to Early Cretaceous - the time of Hogem batholith magmatism. This conclusion contrasts with previous regional tectonic models that suggest Early to Middle Jurassic accretion of Quesnellia onto North American basement. The collision between oceanic arcs and continental margins is generally considered a process that predominates the formation and growth of new continental crust at accretionary orogens. Our combined igneous zircon Hf-O results track the magmatic evolution of the batholith and indicate the importance of juvenile oceanic arcs in contributing crust to the flanks of some accretionary orogens.

Automated summary

New igneous zircon Hf-O data from the Hogem batholith provide insights into the magmatic history and source inputs of the Quesnel arc. The data suggest that mantle-derived magmas were the main contributors to the Hogem batholith, with minor input from young recycled oceanic crust. Contrary to previous models, the study indicates that ancestral North American crust did not play a role in the construction of the Quesnellia region.