Controls on architecture and seismic imaging of igneous intrusions: Examples from LIDAR outcrop data on Traill Ø (East Greenland) and seismic data from the conjugate Møre Margin
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Intrusion of sills into sedimentary successions is a fundamental and widespread process in basins at volcanic rifted margins. Although intrusions emplaced at shallow paleodepths (<1.5 km) are relatively well understood, intrusions emplaced at deeper basinal levels (<1.5 km) are much less understood due to lack of large-scale outcrops and limitation in seismic illumination and resolution. This study makes an attempt to improve the understanding of emplacement mechanisms of deeply emplaced intrusions and how these are controlled by host rock structure and stratigraphy, by using a 25 km long digital outcrop LIDAR model from exceptionally well-exposed outcrops at Traill Ø, East Greenland. This is a world-class outcrop, exposing thick sill intrusions (up to 200 m) emplaced in a complex host rock with faults and variable stratigraphy. Traill Ø shares much of its history with the conjugate Møre Margin on the Norwegian continental shelf, and therefore provides an excellent analogue for understanding igneous sills seen in seismic data from the Møre Basin. Synthetic seismic is compared to seismic data from the Møre Margin to fill the gap between field observations and seismic data. Results show that the emplacement of deeply emplaced sill intrusions (c. 3-4 km) is controlled by host rock lithology, pre-existing structures and the strength of the host rock. Sills show brittle emplacement structures with little deformation around the sill margins despite the intrusions of large amount of sills into the host rock. Sill intrusions seems to prefer extensive mudstone units, thinly interbedded mudstone and sandstone and carbonate/evaporite units. Comparison between outcrop data, synthetic seismic and seismic data can improve the understanding of deeply emplaced sill complexes in the subsurface. Thin sills and steeply dipping intrusions are commonly not imaged in seismic, leading to underestimation of the volume of sills in basins. This study demonstrates the importance of host rock lithology, pre-existing structures and basin history, in order to predict emplacement mechanisms and expression in seismic data of deeply emplaced sill intrusions. Furthermore, it contributes to the understanding of deep sill complexes in sedimentary basins on volcanic margins worldwide.