EGU2020-13768
https://doi.org/10.5194/egusphere-egu2020-13768
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Dyke segmentation: an experimental approach

Maria Jazmin Chàvez-Alvarez and Mariano Cerca-Martìnez
Maria Jazmin Chàvez-Alvarez and Mariano Cerca-Martìnez
  • UNIVERSIDAD NACIONAL AUTONOMA DE MEXICO, CENTRO DE GEOCIENCIAS, Mexico (mjchavez@geociencias.unam.mx)

Hydrofractures induced by a pressurized fluid inside a solid host material occur in nature as joints, veins, and dykes. Due to the heterogeneity of the material properties, rock structure, fluid rheology, and in-situ stress state, the process of hydrofracturing in nature is highly complex. As a result, it is difficult to measure and predict the behavior of natural hydrofractures in field conditions. Fracture segmentation is observed in most materials at every scale from microns to kilometres and dykes are not the exception.  In particular, dykes not always emplace as individual, symmetric and planar structures in the host rock. In many cases even in homogeneous rocks, dykes exhibit segmentation of the type of en chelon-like structures and fingering. The causes of dyke segmentation have been associated with: (1) rock heterogeneity (i.e. pre-existing structures); (2) mixed-mode I+III loading; and (3) instabilities of dike growth process. However, there are still many open questions related to the origin of dyke segmentation, including at which level each of the mentioned processes influences its propagation. In order to have a first approach of study to this phenomenon, a series of laboratory experiments in transparent materials of dyke propagation have been performed. We present the results of experiments of analogue dykes that transport Newtonian and shear thinning fluids that lead to segmentation, in absence of rotational stresses and heterogeneity of the host media. We use these experiments as the most direct source of observations of dike geometry. These experiments allowed the visualization in real time of the developing geometry of the analog dykes and the direction of their propagation.

How to cite: Chàvez-Alvarez, M. J. and Cerca-Martìnez, M.: Dyke segmentation: an experimental approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13768, https://doi.org/10.5194/egusphere-egu2020-13768, 2020

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Presentation version 2 – uploaded on 17 May 2020
The doi for the poster is now correct
  • AC1: Poster available, MARIA JAZMIN CHAVEZ, 18 May 2020

    Chávez, Jazmin (2020), “Dyke segmentation: an experimental approach. ”, Mendeley Data, v1http://dx.doi.org/10.17632/h758kwj57x.1

Presentation version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-13768, Stefano Urbani, 06 May 2020

    Hello Jazmin and Mariano,

    It is a very innovative and interesting work on this topic. 

    I want to ask for some technical questions on the experiments.

    - Which kind of Non-netwonian analogue fluid did you use?

    - Did you have time to do rheometer tests on the non-Newtonian fluids to evaluate the viscosity range that you get in the experiments?

    - Did you notice any significant thickness variation between Newtonian and Non-Newtonian dykes from the profile view images?

    Thanks a lot for your answers.  

    Cheers

    Stefano

    • AC1: Reply to CC1, MARIA JAZMIN CHAVEZ, 07 May 2020

      Hello Stefano, thanks for the interest, we will post soon a poster with details of the work in the doi that appears in the Display's bibliogaphy, you might have a look next week to complement our answer here. 

      - Stefano: Which kind of Non-netwonian analogue fluid did you use?

      Answer: We have used Carbopol® mixed with water at a 0.01% concentration and a density of 1051 kg m-3, Carbopol is a polymer that comes from a family of microgels, made of highly cross-linked poly acrylic acid with a shear thinning behavior that allowed us to model shear thinning magmas.

      - Stefano: Did you have time to do rheometer tests on the non-Newtonian fluids to evaluate the viscosity range that you get in the experiments?

      Answer: Yes, we did rotational and thixotropy tests, at the Anton Paar Laboratory in Mexico City, using a Modular Compact Rheometer (MCR) 302, with a geometry of concentric cylinders (CC-27) of 27 mm of diameter, with a distance among cylinders of 1.1269 mm, on a controlled cell C-PTD 2000 under Peltier controlled temperature fixed at 21ºC. The Carbopol solutions were prepared by mixing manually the powder in distilled water. For the case of rotational tests, the solutions were imposed on an increasing shear rate that went from 1 to 800 s-1. The shear rate incremented linearly in 1200 s, shear strain measurements were taken 40 times each 30 s during the tests. For the thixotropy tests a step test was carried out, i.e. a rotational test with three intervals:  (1) constant low shear rate as in the state at rest, (2) constant high shear rate as applied during flow process, and finally (3) the same shear rate as in the first interval during structural regeneration at rest after application.

      - Stefano: Did you notice any significant thickness variation between Newtonian and Non-Newtonian dykes from the profile view images?

      Answer: Yes, we observed a significant difference. For Newtonian dikes, we have measured a characteristic thickness of 0.002 m while for non-Newtonian experimental dikes the characteristic thickness doubles to 0.004 m.

       

      • CC2: Reply to AC1, Stefano Urbani, 07 May 2020

        Hi,

        Thanks a lot for your answers that are particularly useful for me. I will wait for the poster. 

        Thanks a lot and good luck with this reserach!

        Cheers

  • CC3: Questions and answers from the live chat during EGU2020, Michael Heap, 11 May 2020

    Q: At which dyke propagation stage a significant segmentation occurs? Any idea on the possible causes (e.g. dyke tip acceleration when approaching the free surface)?? Are the Non-Netwonian dykes buoyant?

    A: Segmentation occurs in the last part of the growth stage. Dike segmentation occurs in the last part of growth segmentation stage, when dikes almost reach the surface.

    Q: Lovely models! Have you looked at quantifying the vertical/lateral offset, length, thickness, of segments through time? Also, what do you think, in your models, initiates segmentation?

    A: We have not quantified the offset but we will do it in the future

    Q: Did you manage to add passive markers to any of your analogue experiments to enable visualisation of strain?

    A: We do not have deformation markers for these experiments

    Q: And what is the fluid you used? Was fluid inflow constant or pulsated?

    A: Carbopol. There will be a poster available next week with more details of the work, just follow the link referred in the doi at the Display's supplementary material

    Q: Very interesting models! Do the segments propagate in the same plane or are they slightly offset? Also, do they show any evidence of rotation?

    A: They are offset, sometimes like en echelon segments

    Q: In your models what is the mechanical reason for the segmentation - why, mechanically, does it happen?

    A: Finally, with the same experimental conditions newtonian fluids do not segment in any stage. I end my intervention here, there will be a poster available next week with more details of the work, just follow the link referred in the doi at the Display's supplementary material. Thanks everyone!