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Northeastern Section - 38th Annual Meeting (March 27-29, 2003)

Paper No. 3
Presentation Time: 9:00 AM

BASEMENT BLOCKS IN SOUTHWESTERN CAPE BRETON ISLAND AND ADJACENT MAINLAND NOVA SCOTIA, CANADA, AND THEIR RELATIONSHIP TO THE AVALON TERRANE


WHITE, Chris E., NS Department of Natural Resources, P.O. Box 698, Halifax, NS B3J 2T9, Canada, BARR, Sandra M., Geology, Acadia Univ, Wolfville, NS B4P 2R6, Canada, KETCHUM, John F., Royal Ontario Museum, 100 Queen's Park, Toronto, ON M5S 2C6, Canada and REYNOLDS, Peter H., Earth Sciences, Dalhousie Univ, Halifax, NS B3H 3J5, Canada, whitece@gov.ns.ca

Metamorphic and igneous "basement" rocks are exposed in the Creignish Hills, North Mountain, Sporting Mountain, Cape Porcupine, and Petit-de-Grat areas in southwestern Cape Breton Island and adjacent mainland Nova Scotia. The Creignish Hills and North Mountain blocks consist of low-grade metasedimentary and metavolcanic rocks (Blues Brook and Malagawatch formations), low-pressure amphibolite-facies gneiss and migmatite (Skye Mountain Gneiss and Lime Hill gneiss complex), and ca. 555 Ma dioritic to granitic plutons with calc-alkalic, continental margin arc affinity. These rocks represent the southernmost exposed part of the peri-Gondwanan but non-Avalonian Bras d'Or terrane.

The Sporting Mountain block consists of volcanic and sedimentary rocks intruded by the granodioritic Sporting Mountain Pluton. Lithological similarities and a U-Pb zircon crystallization age of 619 ± 2 Ma for a rhyolite flow confirm that Sporting Mountain block is part of the Mira (=Avalon) terrane of southeastern Cape Breton Island.

The Cape Porcupine block on mainland Nova Scotia consists of relatively undeformed, ca. 610 Ma granite and syenite thrust over mylonitic metasiltstone which yielded 40Ar/39Ar whole-rock ages of ca. 365 Ma. The metasiltstone is in faulted contact with mylonitic metavolcanic and granitoid rocks, the latter with an Early Ordovician U-Pb zircon crystallization age of ca. 480 Ma. The relationship of the Cape Porcupine block to other basement blocks is uncertain.

The Petit-de-Grat block consists of slivers of varied "basement" rocks, including mylonitic granite, amphibolite, and sillimanite-garnet schist, as well as conglomerate and minor basalt intruded by granite, all in faulted contact with younger Carboniferous sedimentary rocks. A U-Pb zircon age of ca. 373 Ma for the undeformed granite and the presence of a contact aureole in adjacent conglomerate are consistent with the interpretation that the conglomerate and basalt are part of the mid-Devonian Guysborough Group of mainland Nova Scotia. The similarity of the metamorphic rocks to basement exposures that are elsewhere associated with the Avalon - Meguma terrane boundary suggests that the Petit-de-Grat area may be part of the Meguma terrane.

Session No. 9

S4. New Developments in Understanding of the Avalon Terrane from the southern Appalachians to Newfoundland I
Thursday, 27 March 2003: 8:15 AM-12:00 PM
Geological Society of America Abstracts with Programs. Vol. 35, No. 3, February 2003, p.17
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