Stress-state evolution of the brittle upper crust during early Variscan tectonic inversion as defined by successive quartz vein types in the High Ardenne slate belt (Germany)

There is a strong interest in processes at the base of the seismogenic crust that can drive fault rupturing and initiate earthquakes. Elevated fluid pressures, in particular, are held responsible for microseismicity at depth as they can overcome the strength of rock and cause natural fractures: a process called hydraulic fracturing. To investigate the role of elevated fluid pressures and the influence of the regional stress state on fracture development, one can study the Earth’s crust either directly by seismological methods or indirectly by investigating natural exhumed fossil analogues in which hydraulic fracturing occurred naturally.


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Figure 1: Process of hydraulic fracturing (NL = 'hydraulische fracturatie')

Figure 2: The Rursee in the North Eifel, Germany. PhD study site with excellent Lower Devonian Geology & tons of veins.

During my PhD research, the Lower Devonian sandstones exposed in the Belgian Ardennes and German North Eifel mountains were studied as they host numerous quartz vein types that were created by hydraulic fracturing at the onset of the Variscan Orogeny (325-300 Ma). The present quartz mineral veins represent sealed fluid pathways and contain valuable information on temperature and pressure changes, and on stress patterns present during fluid flow. Mapping the geometrical interaction of veins with elements such as bedding, cleavage and folds allowed deciphering the precise timing of vein emplacement with respect to deformation. Pressure and temperature (p-T) conditions of veining/fracturing were derived from micro-thermometry of fluid inclusions present in the vein quartz.

Fig. 3: Research methodology

Fig 4: Studied vein types in the High-Ardenne slate belt

Fig. 5: P-T conditions of the two vein types deduced

from fluid inclusion microthermometry

Fig. 6: Studied sites and reconstruction of the stress-state at the time of bedding-normal veining after refolding veins to their original position

Results of this combined research approach showed that elevated (supra)lithostatic fluid pressures are easier to maintain during tectonic inversions, i.e. the stress-state change from extension to compression or vice-versa, than during the main extensional phase of a basin or the contractional phase of an orogeny. In the study area, bedding-normal veins were developed prior to inversion and bedding-parallel veins after inversion. Tectonic inversions are thus crucial timings during which overpressured fluids can be maintained at a regional scale in which the remote state of stress controls the geometry of rock failure. An important discovery was that these coupled changes in stress-states and fluid pressures lead to triaxial stress inversions (Van Noten et al. 2012) and are more complex than the biaxial stress changes in theoretical models. This interaction is important for understanding the genesis of ore deposits as they follow preferential pathways created by the fracture network.

Figure 7: Stress-state evolution of the brittle upper crust illustrated in a brittle failure mode plot. Horizontal scale bar illustrates the differential stress changes during orogeny. Vertical scale bar illustrates the changes in pore-fluid pressure during orogeny. Bedding-normal veins are formed at near-lithostatic pressures. Bedding-parallel veins are formed at supra-lithostatic pressures, able to 'lift up' to rock column.

Figure 8: Thin section of a bedding-parallel quartz vein illustrating the complexity of its formation history: phases of uplift and illustrated by fiber & blocky quartz crystal growth alternated with phases of bedding-parallel shear shown by shear laminae with fine-grained crystals.

Papers resulting from my PhD

The discoveries of my Ph.D. are highlighted in six first author papers cited in various fields. The Van Noten & Sintubin (2010) paper, reporting on the relationship between fracture spacing and bed thickness, influences mechanical fracture development studies. My 2008, 2011 and 2012 papers are cited in numerical and laboratory vein analogue studies and in ore geological studies. As hydraulic fracturing is artificially induced in reservoir exploitation to increase permeability in natural reservoirs, the performed fluid inclusion analysis is particularly useful for a reliable estimate of the p-T conditions present in the seismogenic crust.

    1. Van Noten, K., Sintubin, M. 2019. Unfolding veined fold limbs to deduce a basin’s prefolding state of stress. Chapter in Problems and Solutions in Structural Geology and Tectonics. Elsevier publishing. https://www.elsevier.com/books/problems-and-solutions-in-structural-geology-and-tectonics/billi/978-0-12-814048-2#
    2. Van Noten, K., Van Baelen, H. & Sintubin, M. 2012 The complexity of 3D stress-state changes during compressional tectonic inversion at the onset of orogeny. In: Healy, D., Butler, R.W.H., Shipton, Z.K. & Sibson, R. (Eds) Faulting, Fracturing and Igneous Intrusion in the Earth's Crust. Geological Society, London, Special Publications 367, 51-69. pdf DOI
    3. Van Noten, K., Muchez, Ph. & Sintubin, M. 2011. Stress-state evolution of the brittle upper crust during compressional tectonic inversion as defined by successive quartz vein-types (High-Ardenne slate belt, Germany). Journal of the Geological Society, London 168(2), 407-422. pdf DOI
    4. Van Noten, K., & Sintubin, M. 2010. Linear to non-linear relationship between vein spacing and layer thickness in centimetre- to decimetre-scale siliciclastic multilayers from the High-Ardenne slate belt (Belgium, Germany). Journal of Structural Geology 32(3), 377-391. pdf DOI
    5. Van Noten, K., Berwouts, I., Muchez, Ph. & Sintubin, M. 2009. Evidence of pressure fluctuations recorded in crack-seal veins in low-grade metamorphic siliciclastic metasediments, Late Palaeozoic Rhenohercynian fold-and-thrust belt (Germany). Journal of Geochemical Exploration 101(1), 106. pdf DOI
    6. Van Noten, K., Hilgers, C., Urai, J.L. & Sintubin, M. 2008. Late burial to early tectonic quartz veins in the periphery of the High-Ardenne slate belt (Rursee, North Eifel, Germany). Geologica Belgica 11(3-4), 179-198. pdf DOI

Conference Presentations related to my PhD

  1. Van Noten, K., Van Baelen, H., Berwouts, I. Muchez, Ph., Sintubin, M. 2011. Quartz microstructures as key to unravel orogenic history. Interrelationships between deformation and metamorphism, 23-26 May 2011, Granada, Spain.
  2. Sintubin, M., Van Noten, K., Van Baelen, H. & Muchez, Ph. 2011. Quartz veins as proxy for coupled fluid pressure and stress state evolution at the base of the seismogenic crust: examples from the High-Ardenne Slate Belt (Belgium, Germany, France). DRT Conference, 31 August - 2 September 2011, Oviedo, Spain.
  3. Sintubin, M., Van Baelen, H., Van Noten, K., Schavemaker, Y. & de Bresser, J.H.P. 2011. Kinematic expressions of shear localisation in a slate belt. Examples from the High-Ardenne slate belt (Belgium, France). Penrose Conference: Deformation Localization in Rocks: new advances, 27 June - 2 July 2011, Cadaqués & Cap de Creus peninsula, Catalonia, Spain
  4. Van Noten, K., Van Baelen, H. & Sintubin M. 2011. 3D Stress-State Evolution during Tectonic Inversion. Tectonic Studies Group AGM. 5-7 January 2011, Durham University, Durham, U.K.
  5. Van Noten, K., Van Baelen H., Muchez, Ph. & Sintubin M. 2010. Stress-state evolution of the crust during extensional and compressional tectonic inversion as documented by quartz veins. Anderson Conference: Stress controls on faulting, fracturing and igneous intrusion in the Earth's crust, p18. 6-8 September 2010, Glasgow University, Glasgow, U.K.
  6. Sintubin, M., Van Baelen, H., Van Noten, K. & Muchez, Ph. 2010. Mixed brittle-plastic deformation behaviour at the base of the seismogenic zone as documented by quartz veins (High-Ardenne slate belt, Belgium, Germany). Gordon Research Conference, Transient and transitional behaviour in rock deformation: Moving away from steady-state, 8-13 August 2010, Tilton, NH, USA
  7. Van Noten, K., Muchez., Ph. & Sintubin, M. 2010. The stress state of the brittle upper crust during early Variscan tectonic inversion and its influence on high-pressure compartments. Tectonic Studies Group AGM, 6-8 January 2010, Birmingham University, Birmingham, U.K.
  8. Van Noten, K. 2010. Veins in the High-Ardenne slate belt: useful tools to define early and late orogenic failure. Studiedag: Tectonics and Structural Geology in Belgium. Koninklijke Vlaamse academie voor Wetenschappen en Kunsten (KVAB), 14 May 2010, Brussels, Belgium
  9. Van Noten, K., Muchez, Ph. & Sintubin, M. 2009. Early veining in the Ardenne-Eifel basin (Rursee - Urftsee, Germany): Evidence of tectonic inversion in an overpressured sedimentary basin at the onset of the Variscan Orogeny. 3rd International Conference Geologica Belgica, 54-55, 14-15 September 2009, Ghent, Belgium
  10. Van Noten, K., Berwouts, I., Muchez, Ph. & Sintubin, M. 2009. Evidence of pressure fluctuations recorded in crack-seal veins in low-grade metamorphic siliciclastic metasediments, Late Palaeozoic Rhenohercynian fold-and-thrust belt (Germany). Journal of Geochemical Exploration 101(1), 106. Geofluids, 15-17 April 2009, University of Adelaide, Adelaide, South-Australia
  11. Van Noten, K. & Sintubin, M. 2009. Spatial distribution of quartz veins in alternating siliciclastic sequences and its relationship to bed thickness. Tectonic Studies Group AGM, 27, 7-8 January 2009, Keele University, U.K. ~ Mike Coward Award of best Post-Graduate Talk
  12. Van Noten, K., Hilgers, C., Urai, J.L. & Sintubin, M. 2008. The record of a tectonic inversion in the Lower Devonian Ardenne-Eifel basin (Belgium, Germany): a switch from bedding-normal to bedding-parallel quartz veins. Tectonic Studies Group AGM, 72-73, 8-10 January 2008, La Roche-en-Ardenne, Belgium
  13. Van Noten, K., Kenis, I., Hilgers, C., Urai, J.L. & Sintubin, M. 2007. Early vein generations in the High-Ardenne slate belt (Belgium, Germany): the earliest manifestations of the Variscan orogeny? In: Mechanics of Variscan Orogeny: a modern view on orogenic research. Géologie de la France 2, Orleans, France, 170. 13-15 September 2007, Orleans, France
  14. Van Noten, K., Sintubin, M., Hilgers, C. & Urai, J.L. 2007. On the formation of bedding-perpendicular and bedding-parallel quartz veins in the Variscan fold-and-thrust belt: late burial or early tectonic? Tectonic Studies Group AGM 4-6 January 2007, University of Glasgow, Glasgow, U.K.
  15. Van Noten, K., Kenis, I., Sintubin, M. & Urai, J.L. 2007. Quartz veining in the High-Ardenne slate belt. New evidences from the Rursee area, North Eifel, Germany. Geologica Belgica 10(3-4), 218. Geologica Belgica International Meeting, 7-8 September 2006, Liege, Belgium
  16. Van Noten, K., Kenis, I., Sintubin, M. & Urai, J.L. 2006. Structural morphology and quartz veining in the periphery of the High-Ardenne slate belt, Rursee, North-Eifel, Germany. Tectonic Studies Group AGM, 41, 4-6 January 2006, University of Manchester, Manchester, U.K.