Evidence against large-scale Carboniferous strike-slip faulting in the Appalachian–Caledonian orogen

Abstract

Kent and Opdyke¹ have argued that during the late Devonian and early Carboniferous, the eastern part of the northern Appalachians (Acadia) was situated ∼1,500 km further south relative to cratonic North America than it is at present, and that it moved to its present position sometime later in the Carboniferous (Fig. 1). Van der Voo and Scotese² proposed an even greater displacement of 2,000 km which they attribute to motion between cratonic North America and Europe, Acadia being attached to Europe (Fig. 1). The argument is that palaeolatitudes (λ_p) derived palaeomagnetically from Upper Devonian and Lower Carboniferous rocks of cratonic North America are 15–20° more northerly than those of Acadia and Europe. The proposed shear zone passes through central Newfoundland. Using palaeomagnetic results from eastern and western Newfoundland we show here that no such motion occurred. We also show that Kiaman (late Carboniferous and Permian) overprinting is widespread in Newfoundland, and that these secondary magnetizations agree (with two exceptions attributed to dextral rotation of the Colorado Pleateau) with observations from late Devonian and early Carboniferous rocks of the North American craton, confirming the proposal³ that magnetizations of the cratonic early Carboniferous rocks are Kiaman, not early Carboniferous in age. Our results also enable us to extend this proposal³ to late Devonian rocks of the craton. Hence the palaeolatitudinal offset of Fig. 1 is almost certainly not tectonic, but is an artefact of the wrong assumption of the equivalence of rock and magnetization ages.