Seismic data on the East Shetland Platform, at about 59°50'N 1°12'E, image 4.7–6.6 km of folded possibly Devonian sediments partly coincident with a geophysical anomaly previously interpreted as a granite pluton at shallow depth. Seismic and potential field data constrain the possible distribution of granite, and well data indicate that shallow, lithologidly variable basement rocks may surround the deep ?Devonian basin. Geology Series Halibut Bank and Bressay Bank sheets. It shows the depth in metres below sea level to base Cretaceous, and the location of the northern end of seismicline FGS-64, illustrated in Fig. 3. Good control on the seismic reflectors down to base Jurassic is provided by well3/28-1.

Previous work. Although there is a positive gravity anomaly centred upon the western margin of the East Shetland Platform in block 9/3, Donato & Tully (1982) showed that there is a negative residual gravity anomaly in this area of the East Shetland Platform, when a regional gravity field, based on a model of crustal thinning beneath the Viking Graben, and the gravity effect of the known Tertiary and Mesozoic strata are subtracted from the observed gravity field. They modelled this negative residual gravity anomaly as a granite batholith 40 km in diameter, buried beneath approximately 2 km of sediments, with its centre close to seismic line FGS-64 (Fig.2)

Donato & Tully (1982) also described an associated horseshoe-shaped positive magnetic anomaly around the margins of the negative residual gravity anomaly (Fig. 2). They drew an analogy with Chevoit granite, where similar

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