Anomalous Palaeolatitudes in Cretaceous Granitic Rocks

Abstract

IN a recent study of the distribution of fusulinaceans in western Canada, Monger and Ross¹ interpreted their observations in terms of three plate-tectonic models, two of which invoke or might involve large northward translations of portions of the western Cordillera relative to cratonic North America. In this communication we describe anomalously low palaeomagnetic inclinations in radiometrically dated batholithic rocks exposed in the Cascade Range of central Washington. If interpreted in accordance with the usual axial dipole hypothesis of palaeomagnetism², our results suggest that these rocks originated roughly 25° further from the Cretaceous pole than their present location relative to the North American craton suggests. A simple application of plate tectonics based on existing models^1,3,4 can tentatively account for our results. Alternative explanations seem unlikely.