Fluid flow history from damage zone cements near the Dent and Rawthey faults, NW England

• Published in: Journal of the Geological Society Vol. 165; no. 4; pp. 829 - 837
• Main Authors: Woodcock, N. H, Sayers, N. J, Dickson, J. A. D
• Format: Journal Article
• Language: English
• Published: London Geological Society of London 01.07.2008; The Geological Society of London; Geological Society; Geological Society Publishing House
• Subjects: Askrigg Block; breccia; calcite; carbonates; cement; connectivity; Crystalline rocks; Dent Fault; dilation; dolomite; Earth sciences; Earth, ocean, space; England; Europe; Exact sciences and technology; faults; fluid phase; Geology; Great Britain; hanging wall; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Lake District Massif; meteoric water; orogeny; Paleozoic; Permeability; Plate tectonics; preferential flow; Rawthey Fault; reverse faults; Rocks; sed rocks, sediments; Sedimentary petrology; Structural geology; syntectonic processes; tectonic breccia; topography; United Kingdom; Variscan Orogeny; Western Europe; Alps; Great Britain; Dolomites; Europe; Eastern Alps; England; United Kingdom; Western Europe; damage; Silurian; carbonate rocks; fine-grained materials; lithology; calcite; hanging wall; sulfates; faults; sandstone; drill cores; limestone; silicates; framework silicates; flow; clastic rocks; barite; strain; mudstone; breccia; volcanic rocks; Carboniferous; quartz; Ordovician; igneous rocks; carbonates; Paleozoic; pyroclastics; sedimentary rocks; cement; dilation; upper Paleozoic; brecciation; tuff; dolomite; style
• ISSN: 0016-7649; 2041-479X
• DOI: 10.1144/0016-76492007-133

Fault-related breccias, in Carboniferous limestone, have been well documented in the footwall damage zone to the reverse-oblique Dent Fault. This study describes breccias in the more complicated hanging wall, hosted in pre-deformed Ordovician and Silurian lithologies along the Dent Fault or one of its splays such as the Rawthey Fault. Brecciation style is shown to be influenced by lithology, with the most extensive brecciation in mechanically strong units: siliceous or calcareous mudstone, cemented sandstone and fine tuff. Most brecciation involves dilational strain in the fault damage zones. Attritional breccias are rare, even in fault cores. Dilation breccias are cemented sporadically by quartz or barite, but mostly by carbonate minerals. Transition matrix analysis shows that the sequence of hanging-wall carbonate cements matches that in the footwall: first dolomite or calcite, then ferroan dolomite, then ferroan calcite. This similarity suggests hydrological connectivity from hanging wall to footwall and through tens of cubic kilometres across the Dent-Rawthey fault system. Such connectivity is predicted across upper crustal faults that cut strong mechanical stratigraphy. It is proposed that fluid flow though the fault system was driven mainly by syntectonic topography above the hanging wall, and possibly also by thermal convection caused by a buried granite pluton in the footwall.