Aspects of faulting and fracturing in brittle lithologies

This thesis focuses on aspects of brittle deformation in cohesive lithologies. The pursued concept involves multiscale observations carried out on case studies ranging from satellite images and field outcrops down to the scale of microstructural work to describe and isolate feedback characteristics of brittle failure. Although the collection of observations on fracture geometry and properties is largely static, attempts are made to highlight the evolution of selected properties for the formulation of simple models. Based on theoretical considerations and scaled physical models, the governing parameters of selected feedback systems are analyzed and discussed. The examples shown in this thesis highlight that the evolution of fracture systems shows massive changes in geometry and transport properties over time and emphasizes the importance of negative and positive feedback characteristics.CHAPTER 2 illustrates the development of fault zones in normal faults in overconsolidated claystones of the Variscan Fault- and Thrustbelt. Based on purely mechanical fragmentation, four lithotypes can be identified among normal fault systems that were active during the late stage of exhumation. Although the four lithotypes show a progressive increase in damage, the transport properties – as revealed by SEM analyses and Hg-porosimetry – suggest first a massive increase of permeability, followed by a significant drop with the formation of a tight clay gouge. Although the four lithotypes display successive stages, the heterogeneous occurrences of the different types within the fault zone complicate fault property predictions. This shows that the properties of the fault system can change significantly in space and time.CHAPTER 3 describes the structural inventory and evolutionary stages of an exhumed high-pressure cell in carbonate lithology at Jabal Shams/Oman. The multistage deformation is described by crosscutting relationships of cemented veins and faults. The formation of vein and fault systems is characterized by re-sealing of the fractures by calcite cementation. Although restoring the systems strength to large parts, the successive fracturing events show signs for mechanical interaction, leading to enhanced fragmentation among the fault strands. This well-described example illustrates the importance of mechanical feed-back in a system of constantly restoring strength. The rather isolated field observations of Chapter 3 are extended by a synoptic interpretation of remote sensing data in CHAPTER 4. The interpretation of the fault and fracture network on high-resolution data sets shows that the density of the vein network is not changing significantly with proximity to faults. The density of the fractures is a function of lithological parameters and shows similar densities throughout individual beds. However the densities of individual directional sets yield a patchy distribution. This suggests that a lateral extrapolation of fracture distributions over a large distance is not generally valid as the fractures of individual vein sets in this system may have formed in local events.CHAPTER 5 focuses on a special form of vein texture found in the study area at Jabal Shams. A supersaturated fracture network produces decimeter sized patches of calcite veins within dark carbonate and shows evidence for numerous repeated crack-seal events. As the cement yields a slightly higher strength as the matrix, newly formed fractures form adjacent to pre-existing veins resulting in an anastomosing vein pattern with extremely high fracture densities. Within this framework we discuss the effects of mechanical strength of the matrix, the cement and the interface on fracture localization.CHAPTER 6 discusses the evolution of dilatant fracture volume in a normal fault system of an analogue model. This purely mechanical system is analyzed in 4D with a computer tomograph to obtain visual information on the geometry of the evolving fracture network and to allow statistical analyses on the population of the open-mode volumes over time. It is shown that in a system with natural material heterogeneity the distribution of dilatant jogs yields complex patterns. The first self-similar percolating volume in the experiment illustrates the potential of 3D connectivity of dilatant jogs. The experiment further more shows the interplay of mechanical and geometrical governed systems. As the fractures form in response to the stress field, a discrepancy between the orientation of the fractures and the kinematic framework of the system leads to deformation cycles in which the system is required to constantly adapt. This is reflected by non-linear changes in the fracture volume growth rate and fracture population. Non-linear cycles of rupture and fault growth are in our experiment linked purely to mechanical feedback without the need for additional complexity such as forced-fluid infiltration or chemical alteration due to dissolution and cementation.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2009

Author dc:creator

• Holland, Marc

Contributors dc:contributor

• Urai, János

• info:eu-repo/classification/ddc/550
• Deformation <Geologie>
• Störung
• Carbonate
• Gestein
• Prozess
• Riss
• Geowissenschaften
• Risse
• Spröde
• Gesteine
• Prozesse
• carbonates
• faults
• fractures
• veins
• deformation

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113599%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A51292