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

Abstract:

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.