The thermal impact of Paleocene magmatic underplating in the Faeroe-Shetland-Rockall region
Voluminous magmatism on the northwest European shelf during Palaeogene continental breakup is believed to result in crustal thickening by gabbroic accretion to the base of the crust totalling 4-5 km west of Scotland, 5-8 km around the Faeroe Islands, but only 1-2 km beneath much of the Faeroe-Shetland Basin. Simple models of heat conduction predict high heat-flow (>120mWm -2) following underplating of 5 km of gabbro. This is, however, not substantiated by thermal modelling derived from vitrinite reflectance and apatite fission track data from wells in the Rockall Trough, which show peak heat-flow of <70mWm-2 in the central Rockall Trough and 55-78 mWm-2 in the Faeroe-Shetland Basin. Present day values are 45 mWm-2 and 55-63 mWm-2, respectively. The additional heat-flow is about 60% of that predicted by conduction models assuming instantaneous underplating of a single body. Underplating appears to have taken place progressively over 11 Ma (51-62 Ma) in the form of small plutons, thus reducing the thermal impact compared to an instantaneous event. Nonetheless, variability in underplating is the dominant influence on regional heat-flow and may have had a major impact on source-rock maturation. The oil generating window is predicted to have shallowed by 1.4 km in the northern Rockall Trough in the early Eocene. Present day heat-flow readings indicate that the background heat-flow against which the underplating peak is superimposed increases from 45 mWm-2 in the southern Rockall region, to 50mWm-2 in the northern Rockall, and reaches 55-60mWm-2 in the Faeroe-Shetland Basin. This pattern must reflect changes in the radiogenic content of the underlying crystalline basement and/or its thickness, as most of the underplating-derived heat has now dissipated. © Petroleum Geology '86 Ltd. Published by the Geological Society, London.
Publication Source (Journal or Book title)
Petroleum Geology Conference Proceedings
Clift, P. (1999). The thermal impact of Paleocene magmatic underplating in the Faeroe-Shetland-Rockall region. Petroleum Geology Conference Proceedings, 5, 585-593. https://doi.org/10.1144/0050585