The presence of strata of Westphalian A to possibly Stephanian age in south Staffordshire, located at the southern margin of the Pennine Basin, provides a rare control on the timing of late Carboniferous deformation in Central England. During Westphalian A—C times, sedimentation in south Staffordshire was controlled by thermal subsidence, with a superimposed influence of synsedimentary normal and reverse faulting. Alkaline basic igneous activity occurred during Westphalian C times, synchronous with uplift of the southern margin of the Pennine Basin. Uplift culminated, during Westphalian C—D times, in a phase of Variscan inversion along basement lineaments and the development of a regional unconformity. Renewed subsidence and deposition of a relatively thick sedimentary sequence of Westphalian D to possibly Stephanian age was followed by a final phase of Variscan deformation, comprising possibly two pulses of uplift, tilting and erosion.
Observations presented for south Staffordshire, in conjunction with studies from other parts of the Pennine Basin, indicate a complex interrelationship between rifting, thermal subsidence and Variscan basin inversion. Pulses of N—S extension and E—W to NW—SE compression are interpreted as the product of regional strike-slip deformation, superimposed upon a regime of thermal subsidence. Alkaline igneous activity is considered to be the product of mantle partial melting in response to limited decompression due to transtensional displacements on crustal thickness faults.