the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
20 Jan 2021
20 Jan 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
- 1Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, PA, 18015-3001, United States
- 2Geochronology, Centro Nacional de Investigación de la Evolución Humana (CENIEH) Burgos, 09002, Spain
- 3Idaho Geological Survey, Moscow, ID, 83844-3014, United States
- 4Osservatorio Geologico di Coldigioco, Apiro MC, 62021, Italy
- 5Arizona State University, Tempe, AZ, 85281, United States
- 1Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, PA, 18015-3001, United States
- 2Geochronology, Centro Nacional de Investigación de la Evolución Humana (CENIEH) Burgos, 09002, Spain
- 3Idaho Geological Survey, Moscow, ID, 83844-3014, United States
- 4Osservatorio Geologico di Coldigioco, Apiro MC, 62021, Italy
- 5Arizona State University, Tempe, AZ, 85281, United States
Abstract. The anisotropy of magnetic susceptibility (AMS) technique provides an effective way to measure fabrics and in the process, interpret the kinematics of actively deforming orogens. We collected rock fabric data of alluvial fan sediments surrounding the Sierra Nevada massif, Spain, and a broader range of Cenozoic sediments and rocks across the northern Apennine foreland, Italy, to explore the deformation fabrics that contribute to the ongoing discussions of orogenic kinematics. Sierra Nevada is a regional massif in the hinterland of the Betic Cordillera. We recovered nearly identical kinematics regardless of specimen magnetic minerology, structural position, crustal depth, or time. The principal elongation axes are NE-SW in agreement with mineral lineations, regional GPS geodesy, and seismicity results. The axes trends are consistent with the convergence history of the Africa-Eurasia plate boundary. In Italy, we measured AMS fabrics of specimens collected along a NE-SW corridor spanning the transition from crustal shortening to extension in the northern Apennines. Samples have AMS fabrics compatible only with shortening in the Apennine wedge and have locked in penetrative contractional fabrics, even for those samples that were translated into the actively extending domain. In both regions we found that specimens have a low degree of anisotropy and oblate susceptibility ellipsoids that are consistent with tectonic deformation superposed on compaction fabrics. Collectively, these studies demonstrate the novel ways that AMS can be combined with structural, seismic, and GPS geodetic data to resolve orogenic kinematics in space and time.
David J. Anastasio et al.
Status: final response (author comments only)
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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
- AC1: 'Reply on RC1', Dave Anastasio, 22 Jan 2021
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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
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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.
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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.
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AC3: 'Reply on RC2', Dave Anastasio, 01 Mar 2021
David J. Anastasio et al.
David J. Anastasio et al.
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