ACCRETION AND TECTONIC SETTING OF THE VICTORIA LAKE SUPERGROUP

The Victoria Lake Supergroup (VLS) mainly comprises a southeast-directed thrust stack of four large, distinct slices of Lower Cambrian to lowermost Ordovician arc volcanic rocks that occur immediately east of the Red Indian Line. The basal volcanic rocks of each slice become progressively younger westward and are conformably or disconformably overlain by a Middle to Upper Ordovician cover of volcanic and sedimentary rocks, possibly indicating a Lower Ordovician hiatus. From east to west these slices are the Tally Pond (c. 511 Ma), Long Lake (c. 505 Ma), Tulks Hill (c. 498 Ma) and Pats Pond (c. 488 Ma) assemblages. The Tally Pond assemblage is underlain by exposed c. 560 Ma arc plutons, which combined with the Pb-isotopes in the syngenetic massive sulfides of the VLS indicate a peri-Gondwanan provenance. The age progression of the volcanic slices is most simply explained as a product of westward migration of an eastward-dipping subduction zone (present coordinates) below the Victoria/Penobscot arc outboard of the Gondwanan margin. This arc-trech migration may have been accompanied by opening of one or more marginal basins; the Penobscot ophiolites in the Exploits Subzone (c. 500-490 Ma) may be remnants of such a basin. During Late Ordovician-Silurian collision of the VLS with the peri-Laurentian Harbour Round arc (464-460 Ma), the Lower to Middle Ordovician products of the Victoria arc are inferred to have been largely subducted and buried beneath the Harbour Round arc in central Newfoundland. Remnants of this youngest phase of the Victoria arc are preserved elsewhere.