CARBONIFEROUS JOINTS IN THE NORTH OF ENGLAND AND THEIR RELATION TO EARLIER AND LATER STRUCTURES

Abstract

Summary The orientation of joints in the Carboniferous rocks of extensive areas in the north of England is compared with that in Lower Palaeozoic and Permo-Triassic rocks. The Carboniferous joints have remarkably constant trends, comprising NW., NE. to ENE. and N. sets; they are usually near vertical and at right angles to the bedding. The joints also trend parallel to the faults, but differ from them in inclination; the latter are nearly all normal faults and are believed to have developed later than the joints. The steeper folds and various rock-types are associated with local variations in joint trend, but do not seriously affect the regional pattern. Comparison with adjacent Lower Palaeozoic structures shows that the Carboniferous joint sets are parallel to Caledonian NW. and N. wrench faults and joints, and to the ENE. cleavage; they are thus thought to be inherited from these structures. The Carboniferous structures are considered to have developed in an east-west stress field, with NW. and ENE. joints as sinistral and dextral structures. The Permo-Triassic joint pattern probably originated in the Alpine earth movements, but it is similar to that of the Carboniferous (Variscan) and is considered to have been inherited from the latter, just as the latter was inherited from the Caledonian.