A NEW LOOK AT THE EARLY PALEOZOIC HISTORY OF MEGUMA TERRANE, SOUTHWESTERN NOVA SCOTIA, CANADA

The easternmost tectonic element of the northern Appalachian orogen, the Meguma Terrane of Nova Scotia, includes the Goldenville, Halifax, White Rock and Torbrook formations, intruded by mainly Devonian plutonic units and overlain by Carboniferous and younger rocks. New mapping in the southern part of the terrane has resulted in subdivision of the Goldenville Formation into a lower metasandstone-dominated Green Harbour member and an upper metasandstone/slate Government Point member. The Green Harbour Member contains a distinctive metasiltstone unit with abundant trace fossils including the early Cambrian deep-water ichnofossil Oldhamia, suggesting that the Goldenville Formation below the fossiliferous member likely extends into the Neoproterozoic. The upper part of the formation has yielded a Middle Cambrian trilobite faunule of Acado-Baltic affinity. The overlying slate-rich Halifax Formation has been divided into the Bloomfield, Cunard and Bear River members. The upper part of the Bear River member locally contains Rhabdinopora flabelliformis, an Early Ordovician graptolite, suggesting that underlying Cunard and Bloomfield members are of Late Cambrian age. Both the Goldenville and Halifax formations are locally intruded by swarms of syn-depositional mafic sills of within-plate chemical character, suggesting that if these formations originated in a continental rise prism adjacent to the margin of Gondwana, they began to rift away in the latest Neoproterozoic. Volcanic rocks in the lower part of the overlying White Rock Formation also have within-plate chemical characteristics, and U-Pb ages of ca. 440 Ma, indicating that the base of the formation may extend into only the latest Ordovician. Hence a considerable time gap (ca. 30 - 40 Ma) likely exists between the Halifax and White Rock formations. The White Rock Formation contains Silurian fossils of Rhenish-affinity, and is in gradational contact with the overlying Early Devonian Torbrook Formation which contains both a Rhenish and northern Gondwanan fauna. This gradational change from Rhenish to Gondwanan fauna suggests that the Meguma terrane rifted away from Baltica in the Silurian and drifted towards northwestern Africa or the Iberian Peninsula by the Early Devonian.