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Holdsworth, R. E.
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- PublicationRestrictedDevelopment of interconnected talc networks and weakening of continental low-angle normal faults(2009-06)
; ; ; ; ;Collettini, C.; University of Perugia ;Viti, C.; University of Siena ;Smith, S .A. F; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Holdsworth, R. E.; University of Durham; ; ; Fault zones that slip when oriented at large angles to the maximum compressive stress, i.e., weak faults, represent a signifi cant mechanical problem. Here we document fault weakening induced by dissolution of dolomite and subsequent precipitation of calcite + abundant talc along a low-angle normal fault. Within the fault core, talc forms an interconnected foliated network that deforms by frictional sliding along 50–200-nm-thick talc lamellae. The low frictional strength of talc, combined with dissolution-precipitation creep, can explain slip on low-angle normal faults. In addition, the stable sliding behavior of talc is consistent with the absence of strong earthquakes along such structures. The development of phyllosilicates such as talc by fl uid-assisted processes within fault zones cutting Mg-rich carbonate sequences may be widespread, leading to profound and long-term fault weakness.170 26 - PublicationRestrictedCalibration and validation of reservoir models: the importance of high resolution, quantitative outcrop analogues(2009)
; ; ; ; ; ; ; ; ; ;Jones, R. R.; Geospatial Research Limited, University of Durham ;McCaffrey, K. J. W.; University of Durham ;Imber, J; University of Durham ;Wightman, R.; University of Durham ;Smith, S. A. F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Holdsworth, R. E.; University of Durham ;Clegg, P.; GeoPressure Technology Ltd. ;De Paola, N.; University of Durham ;Healy, D.; University of Durham; ; ; ; ; ; ; ; Rapidly developing methods of digital acquisition, visualization and analysis allow highly detailed outcrop models to be constructed, and used as analogues to provide quantitative information about sedimentological and structural architectures from reservoir to subseismic scales of observation. Terrestrial laser-scanning (lidar) and high precision Real-Time Kinematic GPS are key survey technologies for data acquisition. 3D visualization facilities are used when analysing the outcrop data. Analysis of laser-scan data involves picking of the point-cloud to derive interpolated stratigraphic and structural surfaces. The resultant data can be used as input for object-based models, or can be cellularized and upscaled for use in grid-based reservoir modelling. Outcrop data can also be used to calibrate numerical models of geological processes such as the development and growth of folds, and the initiation and propagation of fractures.165 24 - PublicationRestrictedFault weakening due to CO2 degassing in the Northern Apennines: short- and long-term processes(2008)
; ; ; ; ; ; ;Collettini, C.; Dipartimento di Scienze della Terra, Universita` di Perugia, Piazza dell’Universita` 1, 06100 Perugia, Italy ;Cardellini, C.; Dipartimento di Scienze della Terra, Universita` di Perugia, Piazza dell’Universita 1, 06100 Perugia ;Chiodini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;De Paola, N.; 1Dipartimento di Scienze della Terra, Universita` di Perugia, Piazza dell’Universita1, 06100 Perugia ;Holdsworth, R. E.; Reactivation Research Group, Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK ;Smith, S. A. F.; Reactivation Research Group, Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK; ; ; ; ; The influx of fluids into fault zones can trigger two main types of weakening process that operate over different timescales and facilitate fault movement and earthquake nucleation. Short- and long-term weakening mechanisms along faults require a continuous fluid supply near the base of the brittle crust, a condition satisfied in the extended/extending area of the Northern Apennines of Italy. Here carbon mass balance calculations, coupling aquifer geochemistry to isotopic and hydrological data, define the presence of a large flux (c. 12 160 t/day) of deep-seated CO2 centred in the extended sector of the area. In the currently active extending area, CO2 fluid overpressures at 85% of the lithostatic load have been documented in two deep (4–5 km) boreholes. In the long-term, field studies on an exhumed regional low-angle normal fault show that, during the entire fault history, fluids reacted with fine-grained cataclasites in the fault core to produce aggregates of weak, phyllosilicate-rich fault rocks that deform by fluid assisted frictional–viscous creep at sub-Byerlee friction values (m , 0.3). In the short term, fluids can be stored in structural traps, such as beneath mature faults, and stratigraphical traps such as Triassic evaporites. Both examples preserve evidence for multiple episodes of hydrofracturing induced by short-term cycles of fluid pressure build-up and release. Geochemical data on the regional-scale CO2 degassing process can therefore be related to field observations on fluid rock interactions to provide new insights into the deformation processes responsible for active seismicity in the Northern Apennines234 37 - PublicationRestrictedInteractions between low-angle normal faults and plutonism in the upper crust: Insights from the Island of Elba, Italy(2011)
; ; ; ;Smith, S. A. F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Holdsworth, R. E. ;Collettini, C.; ;low-angle normal fault on the Island of Elba, Italy, was one of the principal structures active during extensional collapse of the Apennine fold-and-thrust belt. We investigate the relationships among the Zuccale fault, subsidiary footwall fault networks, and igneous bodies that were intruded into the immediate footwall of the Zuccale fault. Both brittle and ductile kinematic indicators found in association with fault zones and igneous bodies yield a consistent WNW-ESE extension direction, suggesting that faulting and intrusion overlapped in time. Structure contour analysis indicates that the Zuccale fault has a regional domal morphology. The dimensions and spatial location of the dome correlate with the likely subsurface position of the Porto Azzurro pluton, originally intruded at ~6 km depth. We propose that doming of the Zuccale fault may have been related in part to emplacement of the Porto Azzurro pluton as a tabular intrusion, involving some component of vertical infl ation and roof uplift. The immediate footwall of the Zuccale fault is everywhere crosscut by a complex, linked network of high- and low-angle extensional faults with observed displacements of <10 m. Mutual crosscutting relationships suggest that low- and high-angle faults were active broadly contemporaneously. The fi - nal geometry of the footwall fault networks is adequately explained by their position with respect to the regional domal structure, and they suggest that certain sections of the Zuccale fault were back-rotated—during doming—out of an orientation capable of accommodating continued regional extension.134 19