Secondary magnetization of Triassic‐Jurassic volcaniclastic rocks of the Quesnel Terrane, Quesnel Lake, B.C.

Abstract

Upper Triassic‐Lower Jurassic rocks at Quesnel Lake form part of the Quesnel terrane, which was emplaced against the Omineca Belt, part of the North American (paleo‐)continental margin, in the late Early Jurassic. Hard magnetizations, which may or may not be primary, were identified in volcanic wackes, but they are poorly grouped. However, removed magnetizations of intermediate unblocking temperatures (200‐500°C) and coercivities (30‐50 mT) are systematically directed northeast and downward (D=35°, I=57°, a95=9° 5 sites, 22 specimens; paleopole 62°N, 15°W, dm=13°, dp=10°) with respect to present horizontal. We interpret this to be an overprint, acquired after Middle to Late Jurassic folding, as a result of mid‐Cretaceous plutonism during the Cretaceous Normal Superchron. The paleopole is compatible with Early to mid‐Cretaceous paleopoles from other terranes in the southern Canadian Cordillera, but does not agree with observations from post‐Jurassic cratonic rocks. This disagreement indicates that in the mid‐Cretaceous these terranes, along with at least part of the Omineca Belt to which they were attached, formed a quasi‐rigid super‐terrane which was situated about 2000 km farther south than its present position relative to the craton.