Elsevier

Journal of Structural Geology

Volume 32, Issue 9, September 2010, Pages 1349-1362
Journal of Structural Geology

Analysis of the internal structure of a carbonate damage zone: Implications for the mechanisms of fault breccia formation and fluid flow

https://doi.org/10.1016/j.jsg.2009.04.014Get rights and content

Abstract

A segment of the Salzach-Ennstal fault zone (Talhof fault, Eastern Alps) shows evidence for joint nucleation by layer-parallel shear, causing the formation of joint-bounded slices oriented at high angles (65–85°) with respect to the shear zone boundary (SZB). Subsequent slice rotation resulted in joint reactivation as antithetic shears, slice kinking, and breaking-up of the individual slices into smaller fragments. The latter process, due to the longitudinal constraint of slices with impeded shear zone widening, marked the transition to cataclasite formation and fault core evolution during shear localization. Cataclasites were subsequently cemented and underwent continuous shear deformation by re-fracturing. Cement precipitation from fluids therefore played a fundamental role in the evolution of the fault zone, with a cyclic change between an open and a closed permeability system during fault evolution. Stable isotope compositions (δ13C, δ18O) of fault rock cements indicate a continuous equilibration between protolith-derived fragments and cements precipitated from those fluids. This points to limited fluid amounts, only temporally replenished by meteoric water, and a hydraulic gradient that directed fluid flow from the damage zone towards the fault core.

Introduction

Knowledge of the internal structure of brittle fault zones has been gathered from both field studies (e.g., Anderson, 1951, Tchalenko, 1970, Sibson, 1986, Chester and Logan, 1987, Chester et al., 1993, Caine et al., 1996, Billi et al., 2003, Faulkner et al., 2003, Wibberley and Shimamoto, 2003), and laboratory experiments (e.g., Riedel, 1929, Reches, 1978, Reches, 1983, Logan et al., 1979, Logan et al., 1992, Reches and Dietrich, 1983, Chester and Logan, 1990, Sagy et al., 2001, Katz et al., 2003). Fluid infiltration into faults, and the subsequent fluid–rock interaction, influence the fault mechanical behaviour (Hubbert and Rubey, 1959, Janssen et al., 1998, Kurz et al., 2008). Characterization of the internal structure of fault zones is an essential pre-requisite to understanding and predicting their mechanical, hydraulic and seismic properties (e.g., Faulkner et al., 2003, Woodcock et al., 2007). Generally, the following structural elements may be discriminated across brittle fault zones (following Chester and Logan, 1986, Caine et al., 1996, Caine and Foster, 1999, Billi et al., 2003, Faulkner et al., 2003):

  • (1)

    The host rock, or protolith, consists of the rock mass bounding the fault-related structures.

  • (2)

    The damage zone is characterized by secondary faults of small displacement, veins, and networks of shear and extensional fractures generally related to the processes of fault growth. Generally, the transition from the host rock to the damage zone is quite gradual.

  • (3)

    The fault core is where shear displacement is localized. The core is associated with the development of fault rocks by bulk crushing, particle rotation, abrasion and grain size diminution that obliterate the original host rock fabric (e.g., Billi et al., 2003, Billi et al., 2003, Storti et al., 2003, Billi and Storti, 2004, Billi, 2005, Billi, 2007).

  • (4)

    Following the definition of Vermilye and Scholz (1998), the process zone comprises those features that result directly from propagation of the fault tip. As the damage zone, the process zone is characterized by secondary faults of minor displacement, veins, and networks of shear and extensional fractures. It may overlap with the damage zone as well as with parts of the fault core.

The damage zone and the fault core may also be seen as representing the evolutionary steps of fault development. As the fault core evolves continuously within the damage zone (e.g., Billi et al., 2003, Faulkner et al., 2003), the spatial zoning from the protolith to the core, including the development of fault rocks, corresponds to these evolutionary steps (e.g., Micarelli et al., 2006).

Section snippets

Objectives

In this study we discuss the structural evolution of carbonate fault rocks along a major fault zone in the Eastern Alps, and its implications for fluid flow and the permeability evolution within and along the fault zone. As fault zones highly affect the hydrogeological properties of the rock mass, we will discuss the role of fluids for fault zone evolution, and the interaction of these fluid phases with adjacent rocks. Information on these processes can be obtained from stable isotope

Methods of structural analysis

Samples were taken from the damage zone towards the fault core in order to infer the evolution of structures as displacement increases. Samples were saw-cut into serial sections parallel to the local direction of shear, and perpendicular to the shear zone boundary (SZB). The saw-cut sample sections were stained with black ink and subsequently polished in order to highlight the traces of the fracture network, voids and pores.

We describe the brittle structures by considering their orientation

Geological and tectonic setting

We selected well exposed sites along the Talhof fault (Gmeindl, 1999), which is a 15 km long segment of the Salzach-Ennstal-Mariazell-Puchberg (SEMP) fault system in the Eastern Alps (Fig. 1) (Ratschbacher et al., 1989, Ratschbacher et al., 1991, Decker et al., 1993, Decker and Peresson, 1996, Wang and Neubauer, 1998, Frisch et al., 2000). The WSW–ENE oriented SEMP fault extends for 400 km along the Eastern Alps. The maximum left-lateral displacement along the SEMP is 70 km (Linzer et al., 2002).

Site description

The sites described in this study provide a nearly complete exposure of the Talhof fault segment, i.e. from the protolith to the fault core. Special emphasis will be given on a site exposing the intersection of the Talhof and Giessgraben fault zones (Fig. 3). At the Talhof–Giessgraben fault intersection (Fig. 2), Lower Triassic (Anisian) fine-grained layered marbles are separated from quartzites of Permian to Triassic protolith age, both belonging to the Lower Austro-Alpine unit (Fig. 1).

Evolution of joints and shear fractures at the damage zone–fault core transition

Rocks of the damage zone adjacent to domain 1 are characterized by fractures at high (50–120°) and low (10–30°) angles anticlockwise from to the shear zone boundary. In this study, these fractures are named as high- and low-angle fractures, respectively. The relative timing of fracture formation can be determined by abutting and crosscutting relationships.

Low-angle fractures at angles between 20 and 30°, measured in an anticlockwise sense to the SZB, are sheared fractures. Structures at angles

Fault rocks along the damage zone–fault core boundary

The fault rocks (coarse-grained cataclasite, fault breccia) are characterized by an irregular grain size distribution (Fig. 9, Fig. 10). Sample SHWK2 is entirely made up of a medium-grained cemented cataclasite. Sample Talhof5 is characterized by two distinct domains (Fig. 9). The portions immediately adjacent to the fault plane consist of medium-grained carbonate cataclasites, while those near the damage zone grade into a grain-supported fault breccia. Remnants of former joint-bounded slices

Oxygen and carbon stable isotope compositions

Powder samples were obtained by microdrilling of the rock specimens described above. These samples were analysed using stable isotope geochemistry in order to determine the isotopic composition of (1) host rock-derived slices within the damage zone (Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9), of (2) cataclasite fragments and of (3) fault rock cements (Fig. 9). The analytical techniques are described in the Appendix. Carbon and oxygen isotopic ratios are plotted in Fig. 11 and listed in

Implications for the formation of carbonate fault rocks

The structural evolution presented in this study (Fig. 12) is that fault zone development within layered carbonates starts with shearing of the primary composite foliation. This includes cross jointing between layer-parallel shears (Fig. 12a, b). These joints form a penetrative fabric in terms of a fracture cleavage, which is in contrast to some previous examples (e.g., Wilcox et al., 1973, Paterson, 1978, Olson and Pollard, 1991, Davis et al., 1999, Mandl, 2005). Example: (1) high-angle

Conclusions

  • (1)

    In layered rocks, formation of cataclastic shear zones may start with layer parallel shear and the development of cross-joints at high angles to the shear zone boundary (SZB). This results in the formation of joint-bounded, closely spaced slices, forming a penetrative fabric (fracture cleavage) at the scale of the shear zone.

  • (2)

    The formation of slices bounded by en-echelon joints at high angle to the SZB was probably related to the high ratio of effective normal stresses acting orthogonal to the

Acknowledgements

This study has been carried out during a research project (P 17697-N10) granted by the Austrian Science Fund (FWF). The formal reviews by David Peacock and Fabrizio Storti contributed a lot to the improvement of the first manuscript version. Fabrizio Agosta and Emanuele Tondi are thanked for their thorough editorial comments.

References (91)

  • D.R. Faulkner et al.

    On the internal structure and mechanics of large strike-slip fault zones: field observations of the Carboneras fault in southeastern Spain

    Tectonophysics

    (2003)
  • W. Frisch et al.

    Post-collisional orogen-parallel large-scale extension in the Eastern Alps

    Tectonophysics

    (2000)
  • J.F. Gamond

    Displacement features associated with fault zones: a comparison between observed examples and experimental models

    Journal of Structural Geology

    (1983)
  • J.F. Gamond

    Bridge structures as sense of displacement in brittle fault zones

    Journal of Structural Geology

    (1987)
  • C. Janssen et al.

    Fluid regime in faulting deformation of the Waratah Fault Zone, Australia, as inferred from major and minor element analyses and stable isotope signatures

    Tectonophysics

    (1998)
  • O. Katz et al.

    Faults and their associated host rock deformation: part I. Structure of small faults in a quartz-syenite body, southern Israel

    Journal of Structural Geology

    (2003)
  • Y. Katz et al.

    Geometry and kinematic evolution of Riedel shear structures, Capitol Reef National Park, Utah

    Journal of Structural Geology

    (2004)
  • L.A. Kennedy et al.

    Microstructures of cataclasites in a limestone-on-shale thrust fault: implications for low-temperature recrystallisation of calcite

    Tectonophysics

    (1998)
  • H.-G. Linzer et al.

    Balancing lateral orogenic float of the Eastern Alps

    Tectonophysics

    (2002)
  • J.M. Logan et al.

    Fabrics of experimental fault zones: their development and relationship to mechanical behaviour

  • D. Marquer et al.

    Fluid circulation, progressive deformation and mass-transfer processes in the upper crust: the example of basement–cover relationships in the External Crystalline Massifs, Switzerland

    Journal of Structural Geology

    (1992)
  • S. Mazzoli et al.

    Very low temperature, natural deformation of fine-grained limestone: a case study from the Lucania region, southern Apennines, Italy

    Geodinamica Acta

    (2001)
  • W.D. Means

    Shear zones and rock history

    Tectonophysics

    (1995)
  • L. Micarelli et al.

    Influence of P/T conditions on the style of normal fault initiation and growth in limestones from the SE-Basin, France

    Journal of Structural Geology

    (2005)
  • L. Micarelli et al.

    Structural evolution and permeability of normal fault zones in highly porous carbonate rocks

    Journal of Structural Geology

    (2006)
  • P.N. Mollema et al.

    Development of strike-slip faults in the dolomites of the Sella Group, Northern Italy

    Journal of Structural Geology

    (1999)
  • M.A. Naylor et al.

    Fault geometries in basement-induced wrench faulting under different initial stress states

    Journal of Structural Geology

    (1986)
  • J.-P. Petit et al.

    ‘Crack-seal’, slip: a new fault valve mechanism?

    Journal of Structural Geology

    (1999)
  • E. Pili et al.

    Carbon–oxygen isotope and trace element constraints on how fluids percolate faulted limestones from the San Andreas Fault system: partitioning of fluid sources and pathways

    Chemical Geology

    (2002)
  • Z. Reches

    Analyses of faulting in three-dimensional strain field

    Tectonophysics

    (1978)
  • Z. Reches

    Faulting of rocks in three-dimensional strain fields; II: theoretical analyses

    Tectonophysics

    (1983)
  • Z. Reches et al.

    Faulting of rocks in three-dimensional strain fields; I. Failured rocks in polyaxial, servo-control experiments

    Tectonophysics

    (1983)
  • A. Sagy et al.

    Dynamic fracturing: field and experimental observations

    Journal of Structural Geology

    (2001)
  • R.H. Sibson

    Implications on fault-valve behaviour for rupture nucleation and recurrence

    Tectonophysics

    (1992)
  • R.H. Sibson

    Structural permeability of fluid-driven fault-fracture meshes

    Journal of Structural Geology

    (1996)
  • S.A.F. Smith et al.

    Recognizing the seismic cycle along ancient faults: CO2-induced fluidization of breccias in the footwall of a sealing low-angle normal fault

    Journal of Structural Geology

    (2008)
  • F. Storti et al.

    Particle size distributions in natural carbonate fault rocks: insights for non-self-similar cataclasis

    Earth and Planetary Science Letters

    (2003)
  • E. Tenthorey et al.

    Evolution of strength recovery and permeability during fluid–rock reaction in experimental fault zones

    Earth and Planetary Science Letters

    (2003)
  • X. Wang et al.

    Orogen-parallel strike-slip faults bordering metamorphic core complexes: the Salzach-Enns fault zone in the Eastern Alps, Austria

    Journal of Structural Geology

    (1998)
  • C.A.J. Wibberley et al.

    Internal structure and permeability of major strike-slip fault zones: the Median Tectonic Line in Mie Prefecture, Southwest Japan

    Journal of Structural Geology

    (2003)
  • C.A.J. Wibberley et al.

    Micromechanics of shear rupture and the control of normal stress

    Journal of Structural Geology

    (2000)
  • E.J.M. Willemse et al.

    Nucleation and growth of strike-slip faults in limestones from Somerset, U.K

    Journal of Structural Geology

    (1997)
  • F. Agosta et al.

    Fluid conduits in carbonate-hosted seismogenic normal faults of central Italy

    Journal of Geophysical Research

    (2003)
  • E.M. Anderson

    The Dynamics of Faulting

    (1951)
  • A. Billi et al.

    Particle size distributions of fault rocks and fault transgression: are they related?

    Terra Nova

    (2003)
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