Application of anisotropy of magnetic susceptibility (AMS) fabrics to determine the kinematics of active tectonics: examples from the Betic Cordillera, Spain, and the Northern Apennines, Italy

Anastasio, David J.; Pazzaglia, Frank J.; Parés, Josep M.; Kodama, Kenneth P.; Berti, Claudio; Fisher, James A.; Montanari, Alessandro; Carnes, Lorraine K.

doi:https://doi.org/10.5194/se-12-1125-2021

Articles | Volume 12, issue 5

https://doi.org/10.5194/se-12-1125-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

Tools, data and models for 3-D seismotectonics: Italy as a...

https://doi.org/10.5194/se-12-1125-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 12, issue 5

Research article

|

19 May 2021

Research article |

| 19 May 2021

Application of anisotropy of magnetic susceptibility (AMS) fabrics to determine the kinematics of active tectonics: examples from the Betic Cordillera, Spain, and the Northern Apennines, Italy

David J. Anastasio, Frank J. Pazzaglia, Josep M. Parés, Kenneth P. Kodama, Claudio Berti, James A. Fisher, Alessandro Montanari, and Lorraine K. Carnes

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Final revised paper (published on 19 May 2021)
Preprint (discussion started on 20 Jan 2021)

Interactive discussion

Status: closed

RC1:
'Comment on se-2020-184', Dario Bilardello, 22 Jan 2021

The manuscript presents a magnetic fabric analysis from two example localities in Spain and Italy, to highlight how AMS may be used in conjunction to other structural, seismic and GPS data to infer kinematic information on different time-scales, and in area affected with complex deformation histories, with changes from compressional to extensional regimes. The study is solid, with objectives, methodology, results and interpretations clearly laid out. In the annotated pdf attached I ask for minor clarifications and make few corrections, motly typos, throughout.

Dario Bilardello

Citation: https://doi.org/10.5194/se-2020-184-RC1
- AC1: 'Reply on RC1', Dave Anastasio, 22 Jan 2021
  
  Dario,
  Thank you for your comments and corrections.
  Dave
  
  Citation: https://doi.org/10.5194/se-2020-184-AC1
- AC2: 'Reply on RC1, Changes keyed to submitted manuscript lines based on review by Dario Biradello', Dave Anastasio, 01 Mar 2021
  
  Changes to Anastasio et al., SE-2020-184-RC1
  Changes based on D. Biardello's review.
  
  Line
  49        suggested change accepted, rewriting from reviewer
  53        suggested change accepted, reference added
  59        accepted, typo
  65        deletion added, manuscript clarified
  67        manuscript clarified
  80        manuscript change made
  93        suggested change accepted
  100     suggested change accepted
  134--   comment accepted
  138      sentence added to caption for figure 5 outlining how paramagnetic and ferromagnetic
              components for rock magnetic mineralogy are determined.
  145      There is no girdle between Kint and Kmin, this has been added to the text for
              clarification.
  183      word choice change, sentence clarified
  200      no change as a result of reviewer comment
  228      accepted
  244      no change made
  247      typo fixed
  248      suggested change accepted
  265      suggested change accepted
  267      I've clarified the manuscript text.
  278      typo fixed
  307      suggested change accepted
  312      suggested change accepted
  313      suggested change accepted
  668      suggested change accepted
  711      clarification sentence added to text, references cited
  715      suggested change accepted
  717      I've changed the figure caption to agree with the figure.
  722      suggested change accepted
  766      typo fixed
  771      suggested change accepted
  773      accepted comment, line deleted as
  
  Citation: https://doi.org/10.5194/se-2020-184-AC2
RC2:
'Comment on se-2020-184', Ruth Soto, 17 Feb 2021

This work presents the application of AMS analysis to infer the kinematics of active orogens. It deals with two examples; the Betics (SE Spain) and the Apennines (Italy). I recommend its publication, but I have found some minor problems before it can be considered for publication.

Ruth Soto

1. General comments:

1.1. The work presents two examples from two orogens showing different tectonic contexts, samples analysed in different laboratories and also shows different magnetic mineralogy analyses. This matter makes difficult the direct comparison of data. Morevover, at its present format showing first the Method, Results and Discussion of Example I (Betics) and then that for Example II (Apennines), the manuscript could look like as two attached works. I think this could be solved focusing the work from a different point of view or selecting only one example and go in depth.

1.2. With respect to AMS data from the Betics, you mention that the orientation of K1 axes (i.e. magnetic lineation) is consistent with (1) the minerals lineations of Martínez-Martínez et al. (2002), which are linked to Middle Miocene-Pliocene low-angle extensional faulting, (2) the GPS geodetic data which shows the direction of convergence of the Betics to stable Africa and (3) Neogene brittle extensional structures and recent seismicity, and all are consistent with the same strain field. These three phenomena correspond to three different tectonic processes. Do you think the magnetic lineation result from the three processes? Or you think it is due only to one process and its orientation coincides with the others? Add a discussion related with the origin of the magnetic lineation found in your study area (e.g. Cifelli et al., 2005).

2. Specific comments:

2.1. In the stereoplots of AMS data, please indicate n (number of specimens).

2.2. Figure 7. I have seen some k1 axes that I have not found on Fig. 3. Please check it.

2.3. Conclusions-Lines 297-298. “The AMS technique provides an effective way to identify both modern and paleo-kinematics from sediments and sedimentary rocks largely independent of the magnetic mineralogy of a specimen”

Specify that this occurs in the two studied examples, it is not a general rule.

3. Technical corrections:

3.1. Line 559-561. This reference is not correct, it lacks Balanyá, J.C. and through the text it should be cited as Martínez-Martínez et al., 2002. Correct it.

3.2. Fig. 3. Indicate what are the numbers 1 to 9 in the leyend or figure caption.

3.3. Figure 13 and its figure caption. 13 is not “Drainage divide”, isn’t it? Check it.

Citation: https://doi.org/10.5194/se-2020-184-RC2
- AC3: 'Reply on RC2', Dave Anastasio, 01 Mar 2021
  
  General Comments
  1.1 Thank you for the comment. However, the co-authors and myself think the main scientific point of the contribution is the value of AMS measurements in young unconsolidated sediments for orogenic studies. Therefore, we see a manuscript strengthening from multiple examples. Previous studies that have used the Paleomagnetism laboratory at Lehigh University (i.e., Spanish data) and the Archeomagnetism Laboratory at CENIEH (i.e., Italizn samples) including:
  
  (1) Kodama, K.P., Anastasio, D.J., Newton, M.L., Pares, J.M., Hinnov, L.A. 2010. High-resolution rock magnetic cyclostratigraphy in an Eocene flysch, Spanish Pyrenees. Geochemistry,Geophysics, Geosystems, v. 11 p. 1-22 QOAA07 doi: 10.1029/2010GC003069.
  
  (2) Carrigan, J.H., Anastasio, D.J., Kodama, K.P., Parés, J.M. 2016. Fault-related fold kinematics
  recorded by terrestrial growth strata, Sant Llorenç de Morunys, Pyrenees Mountains, NE Spain.
  Journal of Structural Geology, v. 91, 161-176. http://dx.doi.org/10.1016/j.jsg.2016.09.003
  
  (3) Anastasio, D.J., Teletzke, A.L., Kodama, K.P., Parés, J.M.C., Gunderson, K.L. 2020. Geologic evolution of the Peña Flexure, Southwestern Pyrenees mountain front, Spain. Journal of Structural Geology. Volume 131, Number 1, paper 103969.
  
  Authors, Kodama, Parés, and Anastasio have an excellent track record in studies using both laboratories and we do not see the use of both laboratories as a reason not to include both field examples.
  
  1.2 Thank you for the comment. It is a difficult question. The magnetic lineation must be younger than the depositional age of the sediments which record it. Therefore, the timing of the lineation cannot be Miocene in age. The AMS is a low strain paleogeodetic indicator that equates to the convergence of Africa and Iberia. It equates most uniformly with the GPS and normal fault seismicity datasets and hence is a paleokinematic indicator The introduction ends with the sentence " In this paper, we show how AMS can extend the temporal reach of GPS geodesy back in time in orogenic studies of the Betic Cordillera, Spain and in the northern Apennines, Italy (e.g., Mattei et al., 2004; Fig. 1)".
  
  Specific comments
  2.1 Thank you for the comment. You are correct, figure 7 was incorrect. Figure 3 is correct and figure 7 has been corrected and replotted. The figures now agree as to their number of specimens measured.
  
  Conclusions, lines 297-298. In our opinion, this is a general rule that goes beyond these studies. We go on to say "Stratigraphically controlled AMS measurements are a deep-time, paleogeodetic technique that can be combined with structural geology, GPS geodesy, and seismic data to collectively describe the kinematics of active orogens and to better understand the nature of seismic hazards. In both the Betic Cordillera (Example I) and northern Apennines (Example II), weak but well-organized penetrative AMS fabrics were recovered from young unconsolidated and unburied rocks that could not be analyzed with more traditional methods."
  
  Technical Corrections
  Comment. Balanya added to Martinez-Martinez et al., 2002 in text and references cited.
  Figure 3 caption now includes geologic units.
  Caption for figure 9 has been clarified.
  Caption for figure 10 have been changes. Legend now agrees with figure and caption.
  
  Citation: https://doi.org/10.5194/se-2020-184-AC3

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Dave Anastasio on behalf of the Authors (11 Mar 2021) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (16 Mar 2021) by Massimiliano Porreca

Dear authors,

taking into account the comments and reviews received by two reviewers, I'm happy to announce that the paper can be accepted for publication to the Special Issue of Solid Earth after minor revision. Here below, the authors can find general and specific comments related to the last version of the revised manuscript.

General comments.
The paper is well written and organized. The authors present two examples where it is possible to retrieve strain information from the magnetic fabric of fine-grained sediments involved in recent tectonic phases. The conclusions are well supported by data that are consistent with other independent observations (e.g. geodetic and seismicity data). All the figures are necessary and useful to describe the case studies.

In the organization of the text and figures, I should suggest to put before the AMS representative data of different age deposits (Example II) and then the summary map of the Northern Apennines with all the magnetic lineations. So, I should first describe the AMS data for different sedimentary sequences (now Fig. 12) and then the map of Northern Apennines with AMS results (now Fig. 10).

Specific comments.
The manuscript is focused on the use of the AMS as a tool for determining deformation history. The method is well known and widely applied in different tectonic and sedimentary settings. There is a wide literature regarding the AMS and therefore some references can be integrated into the text:
- Introduction: some more recent references can be added for “strain data providing deformation history of sediments….”
- Introduction: please cite Sagnotti et al., 1998 in the last sentence. Moreover, a comparison of these new AMS data with Sagnotti’s data deserves a minimum of discussion in chapter 5.4 (see annotated pdf file).
- Cite Cifelli et al., 2005 when the origin of magnetic lineation is discussed (see issue below).

As also suggested by Reviewer#2, a brief discussion about the origin of magnetic lineation in clay sediments could be pertinent in this study. This could be discussed either in the Chapter 4 (The AMS method) or in the Chapter 4.4 where the authors describe the intersection lineation.

I’m quite sceptical when the AMS is applied to alluvial fan sediments (see the last sentence of chapter 4.1 and the second sentence of chapter 4.2). In this case, the transport system can mainly control the AMS fabric rather than the tectonic processes. The authors have to demonstrate case by case no influence of the transport system on the AMS in such kind depositional environments.
In chapter 4.4 the authors indicate that paleocurrent evidence on the AMS fabric is unlikely because the clast imbrications show a prevalent eastward transport direction during deposition. Can the authors exclude a rolling effect on the AMS fabric, i.e., maximum elongation oriented orthogonal to the main transport direction?

Chapter 2. Kinematic studies…
In the last sentence, the authors describe that the sampling was done also in “fluvial siliciclastics…” and also in “Pleistocene fluvial sediments”. Which is the difference between these similar sediments? I have no information about Miocene fluvial deposits in Northern Apennines, but only Pleistocene deposits.

Rock magnetism.
How it is possible to have 100% of ferromagnetic minerals in a sample and no other magnetic grains? Which kind of sediments can carry such an important amount of ferromagnetic grains (i.e. volcanics?).

Also, for Umbria-Marche Apennines (chapter 5.1), I suggest adding Porreca et al. 2018 who provided a recent review of all published subsurface geological reconstructions of this part of the Apennines.

FIGURES and CAPTIONS
Fig. 2. Which is the period covered by the focal mechanism data? I guess that the size of the beach-ball is in proportion to the magnitude.
Fig. 5. What do you mean when you say “The kinematic interpretation is the same in all cases” in the caption of Fig. 5?
Fig. 6. The diagram of Fig. 6a is Km versus Pj, not versus T parameter.
Fig. 10. Which is the period covered by the recorded seismicity compiled by Rovida et al. 2020?
Also, for pre-instrument historical seismicity, it should be better to indicate the time interval.

Table A1.
Please indicate the number of measured specimens for each AMS site.

Other minor observations can be found in the annotated pdf file.

Best regards,
M. Porreca

Comments to the Author: PDF

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AR by Dave Anastasio on behalf of the Authors (23 Mar 2021) Author's response Manuscript

ED: Publish subject to technical corrections (07 Apr 2021) by Massimiliano Porreca

ED: Publish subject to technical corrections (07 Apr 2021) by Federico Rossetti (Executive editor)

AR by Dave Anastasio on behalf of the Authors (08 Apr 2021) Manuscript

Short summary

The anisotropy of magnetic susceptibility (AMS) technique provides an effective way to interpret deforming mountain belts. In both the Betics, Spain, and Apennines, Italy, weak but well-organized AMS fabrics were recovered from young unconsolidated and unburied rocks that could not be analyzed with more traditional methods. Collectively, these studies demonstrate the novel ways that AMS can be combined with other data to resolve earthquake hazards in space and time.