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Geomagnetism Laboratory, Department of Earth Sciences, University of Liverpool, PO Box 147, Liverpool L69 3BX, UK
The palaeomagnetic imprint in the Lewisian metamorphic basement was acquired during early post-Laxfordian times and resides in magnetite-filled microfractures. An early magnetizing event dated c. 1820–1750 Ma was largely overprinted by a second event between 1700 and 1500 Ma which was probably linked to retrogressive amphibolite fades metamorphism. It reaches its greatest intensity in the south of the outcrop while the relict remanence survives most prominently in Scourian terranes. Populations of magnetic components are offset by c. 95 km of (presumed Caledonian) sinistral strike slip in the Minches. Intensities and susceptibilities of magnetization are enhanced in zones of Laxfordian reworking relative to the relict Scourian zones. Their distributions in the Outer Hebrides are reproduced in the Mainland outcrop and can be matched following correction for the same sinistral strike slip. A third line of evidence suggesting this motion is the offset of the deep crustal contribution to the aeromagnetic anomalies. The fault zone accommodating this motion may now be represented by one or more of the low angle detachments bordering the western margin of the Minches Basin. Post-Laxfordian remanences in the Outer Hebrides are rotated by an average of 4° with respect to equivalent vectors on the Mainland and may record later block rotations. A mid-Proterozoic reconstruction of the Lewisian complex derived from the magnetic evidence is presented.
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