The role of Paleocene magmatism in the Tertiary evolution of basins on the NW seaboard

Abstract

The presence of magma within a sedimentary basin can have positive effects on its maturation history, and adverse effects which make imaging the basin structure difficult. Gravity data were modelled to image parts of the Sea of the Hebrides Basin not visible on seismic due to reflective near-surface igneous rocks. Magmatism in the Sea of the Hebrides Basin was short-lived (<5 Ma), but resulted in localized extension of up to 20% by dyke emplacement. The high strain rates are the result of two factors: softening of crustal rocks as a result of increased heat flow; and the development of a linked system of dykes, sills and faults which dissipated variations in strain with depth within the lithosphere. The absence of a relationship between igneous structure and existing basin structure suggests that magmatism may play a similar role in the development of the Faeroe–Shetland Trough and North Shetland Trough, which have similar igneous structures to the Hebrides Basin. Central volcanic complexes in the Hebrides Basin are surrounded by zones of enhanced source rock maturity. Minor intrusions appear to have had little effect on thermal histories due to the incremental nature of their emplacement and the presence of pore waters in the sediments. The large number of variables involved makes it difficult to predict the thermal effects of magmatism in different basins.