Constraints on the Age of Continental Rifting and NE Atlantic “Break-Up” using U-Pb Geochronology of Fault-Hosted Calcite Mineralisation: Faroe Islands, European Atlantic Margin

Friday, 19 December 2014
Nick M W Roberts, NERC Isotope Geosciences Laboratory, Keyworth, NG12, United Kingdom and Richard James Walker, University of Leicester, Leicester, LE1, United Kingdom
Continental basins located along the European Atlantic volcanic passive margin are an increasingly important setting for hydrocarbon exploration. Several recent offshore and onshore studies in the Faroe-Shetland Basin have shown that many faults cut part, or all of the Palaeogene lava sequences together with the rocks in the underlying sedimentary basins. These lava-hosted faults have the potential to act both as fluid traps or migration pathways for hydrocarbon accumulations originating at depth below the volcanic pile. Mapping and structural analysis of calcite-mineralized fault sets developed in the Faroe Islands Basalt Group show systematic cross-cutting relationships, which can be fit to a relative chronology of deformation events that record a multi-phase rift-reorientation through time. The geometry and kinematics of structures recorded on the Faroe Islands indicate that they are coeval with the onset of segmented oceanic-spreading on the Reykjanes, Aegir, and Mohns ridges, currently dated at about 54-51 Ma. This age is regionally poorly constrained, utilizing relative ages of oceanic magnetochrons, in a region where magnetochrons are ambiguous. We present new age constraints for initial continental separation, using U-Pb geochronology of crack-seal calcite veins in the Faroe Islands. Calcite grains were selected for each rift-fault set, and analyzed using LA-ICP-MS. Samples were screened to find closed-system material with abundant uranium, and analyzed for alteration using BSE, CL and charge-coat imaging with an SEM. Initial results reveal that although rift-fault kinematics are consistent with the onset of oceanic spreading, the U-Pb ages are much younger than magnetochron (54 Ma) break-up ages, and imply that oceanic spreading had not established in the Faroes region of the margin until at least 45 Ma. This new data is consistent with models for a remnant continental land bridge linking Greenland and Eurasia well into the Eocene.