Paper No. 64-7
Presentation Time: 2:30 PM
THE CONTROL OF COEVAL REGIONAL STRIKE-SLIP FAULTING ON THE EMPLACEMENT OF THE PALEOCENE IGNEOUS CENTRES OF BRITAIN AND IRELAND
The role(s) of mantle plumes and plate tectonics in the location of volcanic and magmatic activity on Earth is much debated. The British Paleocene Igneous Province (BPIP), a component of the much larger North Atlantic Igneous Province, has provided a particularly important ‘natural laboratory’ for the study of the development of volcanic processes. Magmatism in the BPIP comprises a combination of intrusive and extrusive rocks, including dyke swarms and central igneous complexes. Whilst it has long been recognised that the central igneous complexes appear to be spatially coincident with regional-scale faults and terrane boundaries, a direct genetic link between igneous emplacement and regional-scale faulting has been difficult to establish. In the circumstances, the main control on the location of magmatism has been attributed to the Iceland mantle plume. Here, the integration of new and pre-existing lines of evidence reveals a framework of Paleocene conjugate strike-slip faults which temporally and spatially overlap with the igneous complexes. The transfer of km-scale displacements across geometrical complexities along newly formed NNW-trending dextral and reactivated NE-trending sinistral faults has resulted in transtension and localised dilation. When superimposed on coeval Iceland mantle plume-related upwelling, these structures provided sustained pathways for the flow and emplacement of magma into the upper crust. The development of the conjugate regional faults conforms to broadly N-S shortening and E-W extension attributed to Alpine compression (i.e. the collision of the Eurasian and African plates). This plate-tectonic regime was periodically overwhelmed by plume-attributed NE-SW extension that lead to the widespread intrusion of NW-SE trending dyke swarms. In contrast to their effect on the igneous centres, regional strike-slip faults appear to have exerted little control over dyke emplacement. The location of different elements of the BPIP was hence controlled by the interplay of disparate plume-related and plate-related tectonic forces.