EGU2020-19731
https://doi.org/10.5194/egusphere-egu2020-19731
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Do pre-existing basement structures influence the geometry and growth of normal faults and rifts?

Christopher Jackson1, Luca Collanega2, Thomas Phillips1, Antje Lenhart1, Edoseghe Osagiede3, Catherine Siuda1, Matthew Reeve1, Oliver Duffy1, Rebecca Bell1, Atle Rotevatn3, Craig Magee1, Robert Gawthorpe3, Alexander Coleman1, Paul Whipp1, Thomas Kristensen3, Haakon Fossen3, Anna Breda2, and Nicola Marsh4
Christopher Jackson et al.
  • 1Basins Research Group (BRG), Department of Earth Science & Engineering, Prince Consort Road, London, SW7 2BP, UK
  • 2Dipartimento di Geoscienze, University of Padova, Via G. Gradenigo, 6, 35131 Padova, Italy
  • 3Geodynamics and Basin Studies Group, Department of Earth Science, University of Bergen, 5020 Bergen, Norway
  • 4Aker BP, Føniks, Munkegata 26, Trondheim, Norway

Rifts often evolve on a template of crystalline basement that may contain strong lithological and mechanical heterogeneities related to complex pre-rift tectonic histories. Numerous studies argue that reactivation of such pre-existing structures can influence the geometry and evolution of normal faults and rift physiography. However, in many cases: (i) it is unclear where, if at all, structures at the rift margin continue along-strike below the rift axis; and (ii) the precise geometric and kinematic relationship between pre-existing structures and newly formed normal faults is not well understood. These uncertainties reflect the fact that: (i) potential field data are typically of low-resolution, and thus cannot resolve the detailed morphology of shallow fault networks; (ii) field data cannot provide an accurate 3D image of intra-basement structures and the overlying rift; and (iii) seismic reflection data typically do not image deeply buried intra-basement structures. Understanding the kinematic as well as geometric relationship between intra-basement structures and rift-related fault networks is important for understanding plate motions and for undertaking stress inversions, given that paleo-extension directions (and sigma 3) are, in many rifted provinces, typically thought to lie normal to the dominant fault strike. 

 

We here tackle these problems using subsurface data from the Taranaki Basin, offshore New Zealand, and the northern North Sea, offshore west Norway. Our data provide excellent imaging of shallowly buried intra-basement structures, as well as cover-hosted normal faults and their associated pre- and syn-growth strata. We identify a range of intra-basement structures, both extensional and contractional,, and a range of geometric and kinematic interactions between intra-basement structures and cover normal faults. For example, some of the normal faults are physically connected to intra-basement structures oriented oblique to the regional extension direction. It is notable that, even in cases, intra-basement structures were apparently not extensionally reactivated during the later rift phase. Displacement maxima on cover faults occur at 100-200 m above the crystalline basement-cover interface, suggesting the former did not form due to simple extensional reactivation and upward propagation of pre-existing structures; rather, ‘passive’ basement structures somehow perturbed the regional stress field, leading to the development of normal faults whose strikes mimic those of the underlying pre-existing basement structures. Cover normal faults can also display a range of complex geometries related to the linkage of numerous, originally separate slip surfaces, and upward-bifurcation of strongly segmented fault systems. We also show that the timing of physical linkage between basement and cover structures can be recorded in the geometry of related growth strata, which document the switch from non-rotational to rotational faulting.

 

Our analyses show that km-scale, intra-basement structures can control the nucleation and development of newly formed, rift-related normal faults, most likely due to a local perturbation of the regional stress field. Because of this, simply inverting fault strike for causal extension direction may be incorrect, especially in provinces where pre-existing, intra-basement structures occur. We also show that a detailed kinematic analysis is key to deciphering the temporal as well as the geometric relationships between structures developed at multiple structural levels.

How to cite: Jackson, C., Collanega, L., Phillips, T., Lenhart, A., Osagiede, E., Siuda, C., Reeve, M., Duffy, O., Bell, R., Rotevatn, A., Magee, C., Gawthorpe, R., Coleman, A., Whipp, P., Kristensen, T., Fossen, H., Breda, A., and Marsh, N.: Do pre-existing basement structures influence the geometry and growth of normal faults and rifts?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19731, https://doi.org/10.5194/egusphere-egu2020-19731, 2020

Comments on the presentation

AC: Author Comment | CC: Community Comment | Report abuse

Presentation version 2 – uploaded on 03 May 2020
I have modified some of the presentation notes and added animations
  • CC1: Comment on EGU2020-19731, Chao Lei, 04 May 2020

    Thank you for your presentation. Excellent work on the pre-existing structure in the basin analysis. Could you please have a comment on which pre-exiting structure is important for the subsequent faulting, e.g. faulting, rheology, lithology differences?

  • CC2: Comment on EGU2020-19731, Anne Oldenhage, 04 May 2020

    Hi Cris, interesting presentation! Could you indicate if the depth of the top of the basement (at basin scale) is of a large influence to the fault patterns, observed at the surface? 

    • AC1: Reply to CC2, Christopher Jackson, 04 May 2020

      Hi! Thanks for the question. In all our cases, the pre-existing structures directly sub-crop the crytallline basement-sedimentary cover contact. I could imagine that, in other cases, the pre-existing structures might die-out upwards within the basement, not reaching top-basement. In that case, I'm not too sure what would happen, but I suspect the role of the intra-basement structures would be more limited at the onset of extension.

       

      • CC3: Reply to AC1, Anne Oldenhage, 04 May 2020

        Thank you for your reply Chris! 

        • AC2: Reply to CC3, Christopher Jackson, 04 May 2020

          You're welcome!

  • CC4: Comment on EGU2020-19731, Chao Lei, 04 May 2020

    @Chris, Thanks for your suggested paper. However in our study area, we did not have enough drilling well penetrated into the basement. As the basement of our basins are very deep because of thick sediment.

    • AC3: Reply to CC4, Christopher Jackson, 04 May 2020

      Ah. Yes. That is a problem, although potential field modelling/data could help.

Presentation version 1 – uploaded on 28 Apr 2020
  • CC1: Comment on EGU2020-19731, Sheila Peacock, 29 Apr 2020

    Thanks for your presentation.  I shall have to "hear" your "commentary" on it to get the most out of it.  I wonder if fault reactivation is more a matter of chance than I had thought, for instance the balance between cementation strength and effective stress.  Does the strength of cementation depend on the permeability of the wall rock?  It is easier to glue porous objects, e.g. wood, together - does the same apply to rocks?