Tectonic structure of the “Main Fault” in the Opalinus Clay, Mont Terri rock laboratory (Switzerland)

Jaeggi, David; Laurich, Ben; Nussbaum, Christophe; Schuster, Kristof; Connolly, Peter

doi:10.1007/s00015-016-0243-2

Cited by 34 publications

(18 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1 and 2. The dog-legged section is ''rolledout'' to work in 2D view; this preserves the line length The main tectonic structure intersecting the rock laboratory is the 1-6 m wide ''Main Fault'' and is described in Nussbaum et al (2011) and Jaeggi et al (2017). The significance of the fault for this study is that it is considered as being detached from the upper detachment at the top of the Staffelegg Formation.…”

Section: Initial Boundary Conditions and Modelling Constraintsmentioning

confidence: 99%

Tectonic evolution around the Mont Terri rock laboratory, northwestern Swiss Jura: constraints from kinematic forward modelling

Nussbaum¹,

Kloppenburg²,

Caër

et al. 2017

Swiss J Geosci

Self Cite

View full text Add to dashboard Cite

We propose a geometrically, kinematically, and mechanically viable thin-skinned kinematic forward model for a cross section intersecting the Mont Terri rock laboratory in the frontal-most part of the Jura fold-and-thrust belt, Switzerland. In addition to the available tunnel, borehole, and surface data, initial boundary conditions are crucial constraints for the forward modelling scenarios, especially the inherited topography of the basement and any pre-compressional offset within the Mesozoic sediments. Our kinematic analysis suggests an early-stage formation of the Mont Terri anticline located above ENE-trending, Late Paleozoic extensional faults, followed by back-stepping of the deformation developing the Clos du Doubs and Caquerelle anticlines further south. In this model, the thrust sequence was dictated by the inherited basement faults, which acted as nuclei for the ramps, detached along the basal décollement within the Triassic evaporites. The mechanical viability of both the thrust angles and thrust sequence was demonstrated by applying the limit analysis theory. Despite numerous subsurface geological data, extrapolation of structures to depth remains largely under-constrained. We have tested an alternative model for the same cross section, involving an upper detachment at the top of the Staffelegg Formation that leads to duplication of the sub-Opalinus Clay formations, prior to detachment and thrusting on the Triassic evaporites. This model is geometrically and kinematically viable, but raises mechanical questions. A total displacement of 2.9 and 14.2 km are inferred for the classical and the alternative scenarios, respectively. In the latter, forward modelling implies that material was transported 10.8 km along the upper detachment. It is not yet clear where this shortening might have been accommodated. Despite the differences in structural style, both models show that pre-existing basement structures might have interfered in time and space. Both styles may have played a role, with lateral variation dictated by basement inherited structures.

show abstract

Section: Initial Boundary Conditions and Modelling Constraintsmentioning

confidence: 99%

Tectonic evolution around the Mont Terri rock laboratory, northwestern Swiss Jura: constraints from kinematic forward modelling

Nussbaum¹,

Kloppenburg²,

Caër

et al. 2017

Swiss J Geosci

Self Cite

View full text Add to dashboard Cite

show abstract

“…As its main objective, the MT URL evaluates the long-term safety of radioactive waste disposal. A detailed description on the local geological setting can be found in Nussbaum et al [2011Nussbaum et al [ , 2017, in Jaeggi et al [2017], in Bossart and Thury [2008], and in Becker [2000]. The Main Fault is a low offset (<80 m) reverse fault visible as a 0.8 -3 m wide fault zone in the shaly 10 facies of the Opalinus Clay formation (OPA) at the MT URL.…”

Section: Geology and Sample Originmentioning

confidence: 99%

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

Laurich¹,

Urai²,

Vollmer³

et al. 2017

Preprint

Self Cite

View full text Add to dashboard Cite

Abstract. We studied gouge from an upper-crustal, low offset reverse fault in slightly overconsolidated claystone in the Mont Terri rock laboratory (CH). The laboratory is designed to evaluate the suitability of the Opalinus Clay formation (OPA) to host a repository for radioactive waste. The macroscopically dark gouge displays a matrix-based, P-foliated microfabric bordered and truncated by μm-thin shear zones consisting of aligned clay grains, as shown by BIB-SEM and optical microscopy. TEM-SAED shows evidence for randomly oriented nm-sized clay particles in the gouge matrix, surrounding larger elongated phyllosilicates with a strict P-foliation. For the first time in OPA, we report the occurrence of amorphous SiO2 grains within the gouge. Gouge has lower SEM-visible porosity and almost no calcite grains, compared to undeformed OPA. We present two hypotheses to explain the origin of gouge in the Main Fault: (i) "authigenic generation": fluid-mediated removal of calcite from deforming OPA during shearing, (ii) and "clay smear": mechanical smearing of calcite-poor (yet to be identified) source layers into the fault zone. Based on our data we prefer the first or a combination of both, but more work is needed to resolve this. Microstructures indicate a range of deformation mechanisms including solution-precipitation processes and a gouge which is weaker than OPA because of the lower fraction of hard grains. We infer that the long-term rheology of gouge is more strongly rate-dependent than suggested from laboratory experiments.

show abstract

“…Other aspects appropriate for study using our MSM methods and concepts, such as detection and characterization of fault structures, seismic long-term monitoring to characterise evolution of the EDZ (generation and selfsealing), and evolution of backfill material (sand-bentonite), are presented in other papers in this issue (e.g., Jaeggi et al 2017;Wieczorek et al 2017).…”

Section: Introductionmentioning

confidence: 99%

High-resolution mini-seismic methods applied in the Mont Terri rock laboratory (Switzerland)

Schuster¹,

Amann²,

Yong³

et al. 2017

Mont Terri Rock Laboratory, 20 Years

Self Cite

View full text Add to dashboard Cite

We present several mini-seismic methods developed and applied in recent years in the Mont Terri rock laboratory. All these applications aimed at correlating and interpreting seismically derived parameters with relevant rock-mechanical parameters and findings. The complexity of the local site setting always required very high spatial and parameter resolution. Both, seismic P-and S-wave velocities and dynamic elastic parameters, such as the dynamic Poisson's ratio t dyn and the Young's modulus E dyn , are used to characterise the Opalinus Clay under real in situ conditions. We were able to establish a correlation between static and dynamic elastic Young's moduli. We describe the extremely large, small-scale variability of seismic parameters normal and parallel to the bedding plane orientation and address the question of fracture detection. We also present examples of the characterization of excavation-damaged zones with seismic parameters, including extent as well as degree of damage, and compare these to geological and structural mapping. The evolution of borehole-disturbed zones (BdZ) was deduced from repeating high-resolution borehole measurements. Finally, we quantify seismic anisotropy at dimensions between several cm and tens of m.

show abstract

Tectonic structure of the “Main Fault” in the Opalinus Clay, Mont Terri rock laboratory (Switzerland)

Cited by 34 publications

References 21 publications

Tectonic evolution around the Mont Terri rock laboratory, northwestern Swiss Jura: constraints from kinematic forward modelling

Tectonic evolution around the Mont Terri rock laboratory, northwestern Swiss Jura: constraints from kinematic forward modelling

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

High-resolution mini-seismic methods applied in the Mont Terri rock laboratory (Switzerland)

Contact Info

Product

Resources

About