Cross-Strike Discontinuities (Transverse Zones): Lateral Variations within the Moine Thrust Zone, NW Scotland; the Cantabrian Arc, Northern Spain and Comparisons with Appalachian Transverse Structures

Numerous authors have reported on geometry, kinematics, mechanics and hydrocarbon potential within fold-and-thrust belts. Whilst many works have dealt with palinspastic reconstructions and transport-direction-parallel balanced cross-sections, far fewer have focussed on three-dimensional architecture of fold-and-thrust belts, or examined how lateral variations in thrust architecture in different segments of thrust belts are linked via so-called ‘transverse zones’. Systematic alignments of these lateral structures are suggested to include; 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.

In this work, detailed three-dimensional topologies, geometries and kinematics of selected thrust systems are studied to fully analyse the evolution and cause/effects of lateral changes in thrust belts, in each case integrating the field and three-dimensional model interpretations. Project methodologies incorporate new studies of two well-understood and comprehensively mapped thrust belts; the Achnashellach Culmination/Loch Maree Fault, Moine Thrust Zone, NW Scotland and the Somiedo-Correcillas Unit, Cantabrian Arc, northern Spain. These are compared with structures situated within the Anniston, Bessemer and Harpersville transverse zones, Alabama, Appalachian Thrust Belt.

Findings achieved using branch-line/displacement vector analysis methodologies, stratigraphic separation diagrams, and full, sequential restorations of three-dimensional thrust models using new digital mapping/modelling methodologies, characterise the pre-thrusting template and asses that template’s capacity to control subsequent lateral thrust geometries. Transverse zone structures are greatly dependent upon pre-thrust inheritance structures of the orogenic province. Within the study areas, frontal and/or lateral inheritance structures determine structural styles through the development of lateral ramps, displacement transfer faults and transverse faults, which in turn compartmentalise and segment fold-and-thrust belts creating stratigraphic separations and tectonic structures. Greater understanding of pre-thrust orogenic architecture within fold-and-thrust belts will greatly develop the understanding of global orogenic developments and provide important information for hydrocarbon exploration within potential complex orogenic exploration settings.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California