Measurement of geometry and linkage in vein arrays

Veins in an array are characterised by measurement of their length (L), width (W) and orientation (θ), and by the number (0, 1 or 2) of adjacent veins to which they are linked. Data from a single array (129 veins), and two regions (comprising 146 and 64 arrays) have been measured and analysed. The system for measurement provides a sound basis for the quantitative assessment of both the array geometry and the effects of interaction of adjacent veins. Linkage is achieved by a breaching of the bridges of wall rock between veins, either by extension fractures, shear failure or the development of stylolites. It is primarily controlled by the strain, as measured by vein width. The size and shape of the veins is found to be controlled by two factors: the degree of linkage and the kinematics of the array (transtension/transpression). Interplay of these produces variability both within and between arrays, and this is examined for two large datasets from the Lower Jurassic of Somerset and the Lower Carboniferous of the Gower Peninsula, South Wales.