U-Pb Geochronological Constraints On The Evolution Of The ASPY Terrane, Cape Breton Island: Implications For Relationships Between ASPY And BRAS D'OR Terranes And Ganderia In The Canadian Appalachians

Abstract

New U-Pb zircon ages from nine samples of igneous and sedimentary rocks in the Aspy terrane, Cape Breton Island, show that Neoproterozoic rocks form a major part of the terrane and confirm that the terrane was affected by a major Silurian-Devonian tectonothermal event. A rhyolitic crystal tuff, a leucotonalite pluton and a felsic sheet yield ages of 618.8 ± 0.6 Ma, 619.7 ± 0.9 Ma and 573.5 ± 2.7 Ma, respectively. A metasedimentary unit contains zircon ranging in age from ca. 546 to ca. 1520 Ma. A diorite has an age of 428.6 ± 1.9 Ma, and another diorite unit and a quartz porphyry also have probable Late Silurian ages. A third diorite yields an age of 373.0 ± 0.5 Ma, part of a widespread bimodal igneous event represented by both volcanic and plutonic rocks throughout the Aspy region. Geochronological results and field relationships indicate that the Neoproterozoic rocks are similar to those in the Bras d9Or terrane and form the basement to the (Ordovician-)Silurian rocks in the Aspy terrane, and that the Aspy terrane is probably correlative with rocks in the Hermitage flexure of southern Newfoundland where Silurian metasedimentary and metavolcanic rocks lie unconformably on similar Neoproterozoic rocks. Likely correlative rocks also occur in the Kingston terrane of southern New Brunswick. The results of this study support the idea that the Aspy-Kingston terrane is part of Ganderia and that Neoproterozoic rocks in the Bras d9Or terrane and correlative rocks in southwestern Newfoundland and elsewhere represent exposed basement to Ganderia in the Canadian Appalachians.