POST-ACCRETIONARY GRANITOID-RELATED MINERALIZATION IN THE CANADIAN APPALACHIANS: THE ROLE OF REACTIVATED STRUCTURES AND THE LITHOSPHERIC MANTLE

Post-accretionary granitoids of the Canadian Appalachians are an important polymetallic metallotect (e.g., Sn, W, Mo, Au, In) that includes significant resources such as New Brunswick’s Sisson and Mount Pleasant deposits and Nova Scotia’s East Kemptville deposit. Accretionary orogenic systems like the Canadian Appalachians involve multiple accretionary episodes over a protracted period, resulting in a patchwork of accreted terranes and a complex structural network. While post-accretionary granitoids are widespread in both space and time in accretionary orogens, not all post-orogenic magmatic events are associated with significant polymetallic mineralization. Several new geochronological and geochemical studies of post-accretionary granitoids and new studies on post-accretionary fault reactivation in the Canadian Appalachians merit a review of the orogen’s post-accretionary granitoid record. The spatio-temporal distribution, relationships to (re)activated fault systems, and geochemical characteristics of Late Devonian granitoids in particular point to orogen-wide melting at the base of the crust/uppermost mantle that was channeled by active crustal-scale structures into all accreted terranes. Accompanying significant mineralization in most Late Devonian intrusive suites irrespective of host terrane suggests that mantle-derived magma was a controlling factor in the metal budget. However, the tectonic drivers for the deep-seated melting remain poorly understood, warranting further study into the evolution of the lithospheric mantle during this period.