Inversion of electromagnetic induction data for the Iapetus Suture Zone in the UK

Abstract

The Iapetus Suture Zone (ISZ), corresponding to the join between the European crust of northern England and the North American derived crust of Scotland, has been examined by numerous seismic and induction experiments over a 20 year period. The University of Edinburgh electromagnetic (EM) induction group is in the process of building a database comprising magnetotelluric and magnetic variation stations from this region. In this paper we present 2D inversions of selected induction sites along roughly north-south traverses across the ISZ in northern England and southern Scotland. The first inversion involves both the transverse electric (TE) and transverse magnetic (TM) modes for 10 audio-magnetotelluric (approximately 100-0.1 Hz) sites. Care has been taken to remove the effects of static shifts. This inversion resolves a conductive feature beginning under the southern Northumberland Trough at depths of 10 km, dipping to the south below the Alston Block. In the second inversion, 12 longer-period magnetic variation sites were added to the original data set, improving the resolution of this feature, which correlates well with a dipping bright reflector detected by the North East Coast (NEC) seismic reflection experiment. In addition, the Southern Uplands anomaly is imaged. No north-dipping, mid- to deep-crustal conductor is observed which would correlate to north-dipping Palaeozoic subduction under Laurentia.