THE ESSENTIAL ROLE OF MODERN BEDROCK MAPPING IN TECTONIC INTERPRETATIONS: AN EXAMPLE FROM THE ANTIGONISH HIGHLANDS, NORTHERN MAINLAND NOVA SCOTIA, CANADA

With the 21st century came major advancements in the methods of field data acquisition which greatly enhanced map generation and geological interpretation. These advances included global positioning systems, mobile field computers, and the use of portable XRF and magnetic susceptibility meters. Recent 1:10 000-scale bedrock mapping in the Antigonish Highlands exemplifies the use of these mapping tools to better understand the geology and economic potential of that part of Avalonia, and its significance in the evolution of the northern Appalachian orogen. The oldest units recognized in the Antigonish Highlands are Late Neoproterozoic calc-alkaline volcanic and associated sedimentary rocks of the Keppoch, James River, Livingston Cove, Morar Brook, and Chisholm Brook formations of the Georgeville Group. The dominantly sedimentary Bears Brook formation, previous included in the base of the Ordovician to Devonian Arisaig Group, is lithologically more similar to the older units. This interpretation is further substantiated by previously published detrital zircon U-Pb ages from the redefined Bears Brook formation that indicate pre-590 Ma age. The Georgeville Group is intruded by a suite of ca.605 Ma calc-alkaline, diorite to syenogranite plutonic units many of which were previously considered to be Devonian to Carboniferous in age and some were mapped as volcanic units. The newly defined Iron Brook group in the northern Antigonish Highlands consists of a fault-bound package of sedimentary rocks that has yielded early Cambrian microfossils. The previously interpreted interlayered mafic flows in this group are shown to be mafic sills. The Georgeville and Iron Brook groups are intruded by the previously unrecognized but widespread Ordovician West Barneys River plutonic suite which consists of medium- to coarse-grained syenite to alkali-feldspar granite and gabbro with alkalic chemical character. The plutonic and country rocks are intruded by mafic and felsic dykes and sills. These units were deformed prior to the deposition of the overlying Early Silurian to Early Devonian Arisaig Group. These new field observations and data have dramatically changed the previously accepted geological map and our understanding of Avalonia in the northern Appalachian orogen.