Paper No. 65-7
Presentation Time: 2:30 PM
THE WINEGLASS ASSEMBLAGE, SOUTH-CENTRAL BRITISH COLUMBIA: LATE PERMIAN INTRA-OCEANIC ARC COMPLEX BENEATH THE MESOZOIC CADWALLADER ARC TERRANE
Late Permian rocks of the Wineglass assemblage, and unconformably overlying Late Triassic-Early Jurassic clastic sedimentary rocks, are exposed in a structural window beneath overthrust Cache Creek terrane along the lower Chilcotin River, within the Intermontane Belt of southern British Columbia. The Wineglass assemblage includes basalt, rhyolite and felsic volcaniclastic rocks, and a large tonalite pluton. Rhyolites yielded U-Pb zircon crystallization ages of 259 ±2 Ma and 260.8 ±0.3 Ma, and the pluton yielded a U-Pb zircon crystallization age of 254 ±1.2 Ma. The Wineglass assemblage is correlated with the Kutcho assemblage of northern British Columbia, and the Sitlika assemblage of central British Columbia, on the basis of striking lithologic similarity, overlapping U-Pb zircon ages, and similar relationship to structurally overlying Cache Creek terrane. These assemblages are part of a primitive intra-oceanic arc complex that is exposed intermittently along the western edge of Cache Creek terrane from northern to southern British Columbia. The clastic sedimentary rocks that unconformably overlie the Wineglass assemblage are correlated with the Tyaughton Formation and Ladner Group of Cadwallader terrane, which is exposed mainly in the eastern Coast Belt farther south and comprises Late Triassic to Middle Jurassic sedimentary, volcanic and plutonic rocks interpreted as a volcanic arc and associated clastic apron. Late Permian tonalite that nonconformably underlies Upper Triassic rocks of Cadwallader terrane at one locality in the Coast Belt confirms the presence of a Permian arc complex beneath the Mesozoic rocks. The stacked Permian and Mesozoic arc complexes of Cadwallader terrane bear a strong resemblance to Wallowa terrane, located in the Blue Mountains region of northeastern Oregon and west-central Idaho.