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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

Kelly, Michael J.*1; Clarke, Stuart M.1; Leslie, Graham 2; Williams, Graham 1
(1) Earth Sciences and Geography, Keele University, Keele, United Kingdom.
(2) Murchison House, British Geological Survey, Edinburgh, United Kingdom.

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