Fissure fills along faults: Variscan examples from Gower, South Wales

The extent to which persistent, rather than transient, fissures (wide planar voids) can exist along upper crustal faults is important in assessing fault permeability to mineral and hydrocarbon-bearing fluids. Variscan (late Carboniferous) faults cutting Dinantian (Lower Carboniferous) limestones on...

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Bibliographic Details
Published in:Geological magazine 2009-11, Vol.146 (6), p.890-902
Main Authors: WRIGHT, V., WOODCOCK, N. H., DICKSON, J. A. D.
Format: Article
Language:English
Subjects:
active faults
breccia
Calcite
carbonate rocks
Carboniferous
chemical composition
crust
deformation
Europe
fault breccia
faults
fissures
fluid phase
folds
geochemistry
geometry
Glamorgan Wales
Gower Peninsula
Great Britain
hydrocarbons
limestone
lithostratigraphy
organic compounds
orogeny
Paleozoic
permeability
rock, sediment, soil
sedimentary rocks
South Wales
stratigraphic units
structural analysis
Structural geology
tectonics
United Kingdom
upper crust
Variscan Orogeny
vein
veins
void
Wales
water-rock interaction
Western Europe
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Summary:The extent to which persistent, rather than transient, fissures (wide planar voids) can exist along upper crustal faults is important in assessing fault permeability to mineral and hydrocarbon-bearing fluids. Variscan (late Carboniferous) faults cutting Dinantian (Lower Carboniferous) limestones on the Gower peninsula, South Wales, host clear evidence for fissures up to several metres wide. Evidence includes dendritic hematite growth and elongate calcite growth into open voids, spar ball and cockade breccia formation, laminated sediment infill and void-collapse breccias. Detailed mapping reveals cross-cutting geometries and brecciation of earlier fissure fills, showing that fissures were formed during, rather than after, active faulting. Fissures therefore probably formed by geometric mismatch between displaced fault walls, rather than by solution widening along inactive faults.
ISSN:0016-7568
1469-5081
DOI:10.1017/S001675680999001X