BASEMENT ARCHITECTURE OF THE RIFTED NORTHEAST ATLANTIC MARGIN: EVIDENCE FROM A COMBINED GEOCHRONOLOGY, FISSION-TRACK AND POTENTIAL FIELD STUDY

The submerged Rockall Bank represents a large unstretched crustal block separated from the northern European continental margin by the highly attenuated crust of the Rockall Basin. Examination of the Proterozoic basement geology on the Rockall Bank and that of the continental margin (both offshore and onshore) is being undertaken in order to provide insight into the crustal architecture of this region. Samples from the offshore basement areas are very limited and are being examined by petrographic, geochemical, and isotopic techniques. Apatite fission-track dating and potential field studies of the region are being used to examine the Mesozoic and Tertiary development of these basement blocks and assess their role in margin and basin development.

The Rockall Bank is predominately a juvenile Palaeoproterozoic terrane with U-Pb zircon crystallisation ages of c. 1.75 Ga and Sm-Nd model ages of c. 1.9 Ga. Previous Rb-Sr, K-Ar and Ar-Ar data from the region suggest that the main metamorphic phase was c. 1.6 Ga. A possibly dubious whole rock Ar-Ar ‘Grenville’ age (c. 1.0 Ga) from the most southerly sample has led to the interpolation of the Grenville Front across the Bank. A program of Ar-Ar, Rb-Sr mineral dating and apatite fission-track dating is being used to reassess the thermal history of the bank. The Palaeoproterozoic of the Rockall Bank is similar in age to onshore Proterozoic terranes in Ireland and the UK. Further north the Archaean of the Lewisian Complex is tectonically interleaved with minor amounts of Proterozoic crust both on and off shore. The newly recognised Proterozoic region of the Stanton Banks shows a spread of Sm-Nd model ages from 1.9 to 2.5 Ga. Preliminary whole rock Rb-Sr data suggests a metamorphic event at c. 1.74 Ga. U-Pb zircon , Rb-Sr mineral and apatite fission-track dating are being used to examine the igneous and thermal history of this region

Gravity lineaments (free-air, Bouguer, residual and regional) and magnetic anomalies are being used to constrain the interpolation of onshore faults and lineaments across the Rockall basin through to the Rockall Bank. Fission track data are being acquired to constrain the timing of possible reactivation of basement structures.