Jointing and minor tectonics of the S. Crop of the South Wales Coalfield between Machen and Bridgend

Abstract

AbstractObservations on joints, minor faults and mineral veins at 47 localities along the south and south east crop of the S. Wales Coalfield indicate the presence of a joint system comprised of up to 6 sets of fractures striking at 350°, 330°, 290°, 270°, 250° and 210°. The joint sets are parallel to minor faults of strike and dip‐slip types, whilst minor thrust faults indicate an early phase of sub‐horizontal compression. The joint system is thought to be of tectonic origin and developed early in the deformational history of the area in response to a N‐S compression. Later, dilational episodes facilitated the infilling of mineral veins, with the W.N.W. trending set probably indicating the latest phase of dilation in the area. All structures are considered to be of Armorican age, whilst the marked similarity in the orientation of the joint system to that of the North Crop of the Coalfield suggests that the brittle deformation was relatively homogeneous on both flanks of the Coalfield.