Hybrid veins from the southern margin of the Bristol Channel Basin, UK

Sinistral and dextral en echelon hybrid calcite veins are exposed on the southern margin of the Bristol Channel Basin, North Somerset on a Liassic carbonate platform. These hybrid veins are transitional between pure extensional (mode I) and shear fractures (mode II, mode III) and experienced both extensional and shear displacements during their formation. In the study area they occur in conjugate sets with the conjugate angle ranging between 10° and 50°. Based on the kinematic analysis of these veins a new model for the opening of the Bristol Channel is proposed.