Abstract

A complex suite of microdioritic enclaves exposed in tidal sections along the western margin of the Ross of Mull granite (ROM) Scotland preserve unusual evidence of mingling, incomplete mixing and infiltration processes between contemporaneous acidic and dioritic magmas. Using field, textural and mineralogical criteria, the ROM microdioritic enclaves have been classified into two types: 1) megacrystic and 2) megacrystic free. Megacrystic enclaves are further subdivided on megacrystic assemblage into: a) plagioclase and b) amphibole + K-spar + plagioclase types. Corona and mantling textures are a common feature in all enclave megacrysts. In exceptional circumstances, a pervasive veining of the enclaves by felsic strands composed predominantly of plagioclase (An1-25), have formed complex channel-like morphologies that preserve a relict porosity. These channel networks provide the basis of a simple methodology for estimating key petrophysical characteristics of partially molten (igneous) porous media. By serial sectioning through individual enclaves, we show that the preserved channel (porosity) network is interconnected in three dimensions. Using image analysis techniques, we have estimated the porosity (phi) of individual enclave sections to obtain the variation in porosity with depth. Simple representation of the pore-channel network on a branch and node chart allows useful petrophysical characteristics including the connectivity, genus and tortuosity of the network to be estimated. Computer enhanced reconstructions of the pore network in three dimensions are shown that provide a powerful way of visualising the complex geometries that can arise in porous igneous media.