U-PB (ZIRCON) AGE, PETROLOGY, AND TECTONIC SETTING OF THE CANAAN RIVER PLUTON, SOUTHEASTERN NEW BRUNSWICK, CANADA

The Canaan River pluton comprises megacrystic monzogranite and quartz diorite to monzodiorite exposed in several small inliers on the Carboniferous New Brunswick Platform west of Moncton in southeastern New Brunswick. Its distinctive geophysical signature and borehole data suggest that the Canaan River pluton is part of a large buried felsic to mafic intrusive body that lies at relatively shallow depth beneath flat-lying Pennsylvanian sandstone of the Pictou Group. New LA-ICP-MS in situ analysis of the megacrystic monzogranite yielded a U-Pb zircon concordia age of 412.6 ± 2.1 Ma, indicating that the intrusion was emplaced into rocks of the Kingsclear Group in the Fredericton trough during the Early Devonian (upper Lochkovian). Granitic samples from the Canaan River pluton have negative Nb and Ti anomalies, suggesting a subduction component or assimilation of an upper crustal material, consistent with the positions of most of the samples in the overlapping volcanic-arc and post-collisional granite fields and in the field for slab failure plutons on tectonic setting discrimination diagrams. It was generated in a complex tectonomagmatic setting related to the successive arrival of the leading edge of Ganderia and Avalonia at the composite Laurentian margin during the Salinic and Acadian orogenies. Although its current position immediately west of the Belleisle Fault appears to suggest that the Canaan River pluton is in a tectonostratigraphic position similar to that of the southern parts of the Saint George Batholith and Coastal Maine Magmatic Province, the new age along with lithological, geochemical, and isotopic data suggest that the Canaan River pluton is most like the megacrystic Hawkshaw Granite, also of upper Lochkovian age and part of the Pokiok Batholith farther to the north in the Central plutonic belt of New Brunswick. This interpretation indicates that the older A-type bimodal intrusions of the Saint George Batholith, located proximal to the Acadian suture, have been cut out in the Canaan River area by regional-scale strike slip faulting, thus explaining the termination of the Saint George Batholith and the rest of the Coastal Maine Magmatic Province in southern New Brunswick.