Palaeomagnetism of late Precambrian-Cambrian volcanics and intrusives from the Armorican Massif, France

Abstract

Summary. Results are presented for a magnetotelluric and magnetovariational study in northern Scotland. For nine of the 20 sites at which observations were made the results of the analysis are presented fully together with one-dimensional (1-D) Monte-Carlo inversions for representative sites from the Lewisian Foreland, the North-west Highlands, the Great Glen region and the Grampian Highlands. For the remaining sites, the results are summarized. The 1-D models of all sites situated in a traverse extending from the Lewisian Foreland to the neighbourhood of the Highland Boundary Fault have been used as the basis for preliminary 2-D modelling. Maps of magnetic field induction vectors and transfer functions for an inducing field perpendicular to the average geological strike are presented for periods of 23-819s. The 2-D conductivity models were constrained by both the magnetotelluric and magnetovariational responses. The period range of observation in this study was too limited to resolve structural differences in the upper crust but adequate to reveal a moderately good conductor at upper mantle/lower crustal depths in the Caledonian metamorphic zone. In contrast the whole of the crust in the Lewisian Foreland is highly resistive and there is no evidence of an intermediate conducting layer between the crust and mantle in this region.