INVERSION OF ELECTROMAGNETIC INDUCTION DATA FOR THE IAPETUS SUTURE ZONE IN THE UK

The Iapetus Suture Zone (ISZ), corresponding to the join between the E uropean crust of northern England and the North American derived crust of Scotland, has been examined by numerous seismic and induction expe riments over a 20 year period. The University of Edinburgh electromagn etic (EM) induction group is in the process of building a database com prising magnetotelluric and magnetic variation stations from this regi on. In this paper we present 2D inversions of selected induction sites along roughly north-south traverses across the ISZ in northern Englan d and southern Scotland. The first inversion involves both the transve rse electric (TE) and transverse magnetic (TM) modes for 10 audio-magn etotelluric (approximately 100-0.1 Hz) sites. Care has been taken to r emove the effects of static shifts. This inversion resolves a conducti ve feature beginning under the southern Northumberland Trough at depth s of 10 km, dipping to the south below the Alston Block. In the second inversion, 12 longer-period magnetic variation sites were added to th e original data set, improving the resolution of this feature, which c orrelates well with a dipping bright reflector detected by the North E ast Coast (NEC) seismic reflection experiment. In addition, the Southe rn Uplands anomaly is imaged. No north-dipping, mid-to deep-crustal co nductor is observed which would correlate to north-dipping Palaeozoic subduction under Laurentia.