Keele Research Repository

Abrupt lateral changes in thrust geometry occur in many mountain-building fold-thrust belts. Whilst many works have dealt with palinspastic reconstructions and transport-directionparallel balanced cross-sections, far fewer show a full three-dimensional architecture, or examine how lateral variations in thrust architecture can be linked via cross-strike discontinuities or transverse zones. Systematic alignments of lateral structures are suggested to be related to kinematic responses to irregularities generated across pre-existing, sometimes reactivated, sub-décollement basement faults, pre-thrusting cover strata deformation above basement faults, development of duplex structures / antiformal stacks, and / or along-strike variations in mechanical stratigraphy.

New cross-strike discontinuity / transverse zone identification methodologies developed within this research incorporating thrust ramp-flat alignment analyses and branch-point, cutoff point and fault-tip point analyses, together with a variety of previously utilised identification techniques, allow spatial alignments of lateral structures to be determined. New methodologies help to better characterise the pre-thrust template and assess that template’s capacity to control subsequent lateral thrust geometries on a variety of scales during allochthon formation within two contrasting fold-thrust belts, the linear Moine Thrust Belt and the oroclinal Cantabrian Thrust Belt.

Within the Kinlochewe region of the Moine Thrust Belt, a distinct compartmentalisation is identified across the Loch Maree Fault (LMF). A thrust dominated region of overturned Torridonian / Lewisian, overlying a right-way-up Cambrian succession can be clearly identified on the northern wall of the LMF, compared to a fold-and-thrust dominated section on the southern wall. Compartmentalisation is suggested to be a response to a step in basement that generated a transport-parallel lateral ramp or sidewall during thrusting. A series of potential cross-strike discontinuities / transverse zones are identified within the Cantabrian Thrust Belt. Structural disparities are suggested to have developed as a result of along-strike variations in stratigraphical thickness and regional transport during a multiphase oroclinal development.