A NEW GEOLOGICAL MAP OF THE GANDERIAN ASPY TERRANE, CAPE BRETON HIGHLANDS, NOVA SCOTIA, CANADA

The Aspy terrane in Cape Breton Island preserves a compressed and imbricated assemblage of Ediacaran through Devonian metamorphic and plutonic rocks resulting from its location on the St. Lawrence Promontory and many syn- and post-orogenic faults. New mapping and related studies in the Aspy terrane provide better understanding of the complex history of this small but critical component of Ganderia and demonstrate links to more extensive Ganderia terranes preserved in Newfoundland, New Brunswick, and New England. The Cheticamp block in the western Aspy terrane includes quartzite and marble correlative with similar rocks of Ediacaran age in Bras d'Or terrane and intruded by ca. 560 Ma and Silurian plutons. These rocks are surrounded by Late Devonian bimodal volcanic and sedimentary rocks that obscure their relations with ca. 490-475 Ma arc-related dioritic-tonalitic plutons and overlying Ordovician-Silurian metavolcanic and metasedimentary rocks of the Faribault Brook and Dauphinee Brook formations. The Western Highlands shear zone separates these rocks from the adjacent northwestern highlands block and is “stitched” by the undeformed ca. 375 Ma Salmon Pool gabbro and granite. The northwestern highlands block consists of Ordovician-Silurian high-grade metasedimentary and metaplutonic rocks of the Pleasant Bay Complex (PBC), intruded by ca. 375 Ma mesozonal plutons. The PBC and correlative high-grade metamorphic rocks of the Middle River Formation (MRF) and associated deformed plutons extend into the central highlands where they are in tectonic contact with lower-grade metasedimentary and metavolcanic rocks of the Money Point Group and correlative units. The PBC and correlatives also extend into the northeastern highlands where they are intruded by abundant ca. 415 Ma and 375 Ma mesozonal S-type plutons, the latter of which may “stitch” the tectonic contacts between the low-grade rocks (Money Point Group) and high-grade rocks (Cape North Group). Extensional magmatism began in the western Aspy terrane by 375 Ma but occurred later in the central highlands where late Devonian plutons (e.g., Margaree) intruded at ca. 365-360 Ma. In the southern highlands, a SW-directed thrust of the MRF over Carboniferous rocks confirms late thrusting also documented elsewhere around the Cape Breton Highlands.