Abstract:

There is a basic assumption that the upper crustal point of magma emplacement overlies the point where magma was generated. This contribution discusses the concept of lateral magma movement in the upper crust based on the Mourne Granite Centres, Northern Ireland. We report anisotropy of magnetic susceptibility fabric data from the Western Mourne Centre that indicate SSW to NNE inflow in this centre, parallel to the Eastern Centre. This suggests that these two centres share a common feeder zone outside the Mourne area c. 20 km to the south, coincident with a c. 50 mGal gravity anomaly that may be caused by an unexposed mafic pluton. The links between mafic and felsic magmas in this region, and the coincidence of the projected Mourne granite feeder zone and the possible buried mafic pluton lead to a model in which the Mourne granites were emplaced in a NNE direction as two gently dipping sheets from this unexposed mafic body. From this we develop a model that incorporates existing geophysics and known tectonic framework and involves an interconnected upper crustal network of Early Palaeogene igneous intrusion pathways fed from a common tectonically controlled, and probably long-lived, deeply penetrating feeder zone.

Supplementary material:

Anisotropy of magnetic susceptibility data, thermomagnetic analyses and a thin section showing magnetite in biotite cleavage are available at http://www.geolsoc.org.uk/SUP18458.

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