Multicomponent magnetization in the helmsdale granite, north Scotland; geotectonic implication

A palaeomagnetic study of the Helmsdale granite (U/Pb-420 m.y., K/Ar-400 m.y.), northeast Scotland, has revealed a multicomponent remanence dominated by two characteristic axes of magnetization. The suggested oldest of these magnetizations, the direction of which is nearly horizontal and directed N-S, is thought to have been acquired in Upper Silurian-Lower Devonian times. The existence of this shallow direction of magnetization discounts a recent hypothesis of a ca. 2000 km sinistral offset along the Great Glen Fault. The second component of magnetization appears to be partly carried by haematite that apparently formed through disintegration of biotite and/or plagioclase. This secondary magnetization has a direction that can be associated with a Permian-early Mesozoic age. Similar overprinted magnetizations are characteristic features also in the Devonian sedimentary sequences north of Helmsdale.