Transpressive duplex and flower structure: Dent Fault System, NW England
Nigel Woodcock and Barrie Rickards
Department of Earth Sciences, University of Cambridge,
Downing Street, Cambridge CB2 3EQ, UK
nhw1@esc.cam.ac.uk
Revised mapping of an area along the Dent Fault (northwest England) has improved the resolution of folds and faults formed during Variscan (late Carboniferous) sinistral transpression.
A NNE-trending east-down monocline, comprising the Fell End Syncline and Taythes Anticline, was forced in the Carboniferous cover above a reactivated precursor to the Dent Fault within the Lower Palaeozoic basement. The Taythes Anticline is periclinal due to interference with earlier Acadian folds. The steep limb of the monocline was eventually cut by the west-dipping Dent Fault. The hangingwall of the Dent Fault was dissected by sub-vertical or east dipping faults, together forming a positive flower structure in cross-section and a contractional duplex in plan view. The footwall to the Dent Fault preserves evidence of mostly dip-slip displacements, whereas strike-slip seems to have been preferentially partitioned into the hangingwall faults. This pattern of displacement partitioning may be typical of transpressive structures in general.
The faults of the Taythes duplex formed in a restraining overlap zone between the Dent Fault and the Rawthey Fault to the west. The orientations of the duplex faults were a response to kinematic boundary conditions rather than directly to the regional stress field. Kinematic constraints provide by the Dent and neighbouring Variscan faults yield a NNW-SSE best-fit regional shortening direction in this part of the Variscan foreland.