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Mapping the structure of the Faroe-Shetland Margin using a newly merged high resolution gravity and magnetic dataset

Abstract

The Faroe-Shetland Margin is a challenging exploration environment, complicated by environmental challenges and a long, diverse geological history. The region is inherently structurally complex, having undergone compression during the Caledonian and Variscan orogenies, and several phases of extension and rifting since the middle Paleozoic (Ritchie et al., 2011; Coward et al., 2003). Final breakup between Northwest Europe and Greenland occurred in the Eocene, and was accompanied on the Faroe-Shetland Margin by the emplacement of voluminous basalts, attributed to the North Atlantic Igneous Province (White and McKenzie, 1989).

Seismic imaging of the sub-basalt structural framework on the Margin proves challenging, primarily because of the high impendence contrast between the sediments and shallow basalts, which can cause strong seismic events that obscure deeper and weaker reflections (White et al., 1999). Despite the application of experimental wide-angle seismic reflection studies (e.g. Roberts, White, & Christie, 2009), the deep crustal architecture of the Faroe-Shetland region remains uncertain. Consequently, determining the location, shape and depth of key geological features which underpin hydrocarbon exploration (sedimentary basins, basement highs, and basaltic flows / sills) remains a key objective for the appraisal of hydrocarbon potential and reduction of exploration risk in the region.

Gravity and magnetic data record variations in the density and susceptibility of the entire crust, and are therefore not hindered by the presence of basalts when being used to interpret deeper geological structure. Instead, the principal challenge is to try and distinguish between superposed bodies, with different densities and susceptibilities, from the combined gravity and magnetic anomalies.

In this study, high resolution gravity and magnetic data from PGS and DECC were merged by ARKeX, and used to produce 2D models along several key seismic lines from the PGS FSB MegaSurveyPlus and CRRG-11 seismic surveys. By combining the strengths of seismic data and its interpretation to understand the shallow part of the section, with the strengths of gravity and magnetic data to model the deeper sub-basalt and crustal part of the section, a set of consistent density, velocity and susceptibility models were produced. These models help to assess the contribution of each modelled layer to the gravity and magnetic signal, which can then be used to aid in determining a potential morphology of crystalline basement and likely distribution of igneous bodies/basalts along each line. These observations were then extrapolated, using the merged high resolution datasets and public domain data wherever possible.

We present a new structural and kinematic interpretation of the geology of the region (and potential impacts of this for future exploration), and propose an asymmetric simple shear model for the Faroe-Shetland segment of the UK Atlantic Margin.