Anisotropy of Out-of-Phase Magnetic Susceptibility: A Non-Standard Approach for Magnetic Subfabrics Determination in Variscan Granites of Iberian Massif
Round 1
Reviewer 1 Report
The Phase in sites LM19, LM32 and mainly ASM076 is very low, much lower than the sensitivity in the phase determination presented by the instrument producer (0.1°, see Agico leaflet). Even though the real results are often better than those guaranteed by the producer, I would recommend presenting the results of the opAMS of the above sites more carefully.
Line 114. It should be added n=(n1+n2+n3)/3. K1>K2>K3 cannot be normed, otherwise Km=1. Please, delete the word normed.
Author Response
Dear Reviewer,
Thank you very much for your comments. In the attached document, we explain what we have done.
Best regards,
Cláudia.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper submitted by Cláudia Cruz and coauthors introduces the application of the so-called out of phase AMS (developed by Hrouda et al., 2013 and 2017) to three granitic bodies from NW Iberia. The authors prove the coaxiality of most studied sites (op vs. ip) and conclude that the ferromagnetic fabric is similar to the bulk one, pointing to the mimicry of both fabrics (in terms of Archanjo et al., 1995). The paper proves the suitability of the application of this technique (ip and op AMS) to unravel AMS subfabrics in a quick and resolute way in granitic rocks. The paper is well-written, goes to the point and the discussion and conclusions are well supported by the data introduced in the papers. Therefore, I recommend minor revisions.
Some comments/improvements:
1) The occurrence of magnetite in Portuguese granitoids is not rare (Monchiques; Barbosa, 1999; SIntra, Terrinha, 2018). You may better say in paramagnetic granites but even so, calk-alkaline bodies in NW Iberia, some of them very near some of the studied bodies, have shown evidences of ferromagnetic minerals (Pueyo et al., 1995) as well as in other Variscan granites in the Pyrenean region (Bielsa- Roman-Berdiel et al.,2004; Millares- Roman-Berdiel et al.,2006; Marimanha- Antolín et al., 2009; Mont Louis-Andorra- Pueyo et al., 2022). Therefore, magnetite is present in many Variscan CA bodies, although is likely not significant for AMS studies. Accordingly, this sentence (line #73) must be reformulated and better described/ explained.
SEE ATACHETED PDF FILE
Histograms examples (Left; Pyrenean bodies), Central and right; Sintra granite.
2) In this sense, I wonder if those bodies are really “magnetic” in terms of Ishihara, 1977) or their main distribution is paramagnetic (as many Variscan bodies in NW Iberia; Román-Berdiel, 1995,1998; Aranguren, 1998, 2003; Veiga, Trives, Guitiriz, Tojiza respectively) or as those studied by Helena Sant’Ovaia in other Portugal regions (Sant’Ovaia et al., 2000, 2010 among others). It may happen that the bodies are mostly paramagnetic but some sites are in the ferromagnetic range (in terms of Enkin et al., 2020). To clarify this point, please include a new figure with the susceptibility histograms of the three studied bodies to show their magnetic character. Examples (figure): left: highlighting the paramagnetic part (in terms of Rochette 1987). Central and left: entire distribution of sites. The sole definition of the distribution ranges (lines 146-47; 167-68 and 180-81) is not enough to ensure the magnetic character.
3) Susceptibility units: 10-6 S.I. is a quite standard unit in AMS studies (better than µS.I. or 10-5 S.I.). I would suggest the author to use this standard along the paper (including figures). Additionally, table 1 should include complete directional data K1 dec and inc, E12, etc… for both op-AMS and ip-AMS. Watch out, table 1 layout is currently between two pages
4) Please, enlarge figure 3 considerably, I would even suggest to split in two pages; one page for LM19, 32, 33 and 34 and another for the rest.
5) Figure 1: I do not like, geological maps with political borders (and empty spaces at the other side…), from a geological perspective they are bootless. Please, include a new map of the NW Iberian Variscan geology (like the one used by Sant’Ovaia et al., 2010) and then, if you want, draw the political border.
Minor changes
line #10: remove “name Lastname”
line #33 Oliva-Urcia (not Olivia-Urcia)
line #32-33; maybe the work by Rochette et al., 1992 also merits a citation here…
check lines #44-45 and #49-50; they are repeated
line #83-84: specify the magnetic field used
lines #107-113, a Jelinek’s 1981 citation is here requested, after the definition of those indexes
References:
Antolín-Tomás, B., et al. (2009). Structural and magnetic fabric study of the Marimanha granite (Axial Zone of the Pyrenees). International Journal of Earth Sciences, 98(2), 427-441.
Aranguren, A., et al. (1996). The Guitiriz granite, Variscan belt of northern Spain: extension-controlled emplacement of magma during tectonic escape. Earth and Planetary Science Letters, 139(1-2), 165-176.
Aranguren, A., et al. (2003). Granite laccolith emplacement in the Iberian arc: AMS and gravity study of the La Tojiza pluton (NW Spain). Journal of the Geological Society, 160(3), 435-445.
Archanjo, C. J., Launeau, P., & Bouchez, J. L. (1995). Magnetic fabric vs. magnetite and biotite shape fabrics of the magnetite-bearing granite pluton of Gameleiras (Northeast Brazil). Physics of the Earth and Planetary Interiors, 89(1-2), 63-75.
Barbosa, S. A. (1999). Estudo geoestatístico de dados experimentais da anisotropia da susceptibilidade magnética de rochas do maciço de Monchique.
Enkin, R. J., Hamilton, T. S., & Morris, W. A. (2020). The Henkel Petrophysical plot: Mineralogy and lithology from physical properties. Geochemistry, Geophysics, Geosystems, 21(1), e2019GC008818.
Ishihara, S. (1977). The magnetite-series and ilmenite-series granitic rocks. Mining geology, 27(145), 293-305.
Jelinek, V. (1981). Characterization of the magnetic fabric of rocks. Tectonophysics, 79(3-4), T63-T67.
Oliva-Urcia, B., et al. (2012). On the reliability of AMS in ilmenite-type granites: an insight from the Marimanha pluton, Central Pyrenees. Geophysical Journal International, 189(1), 187-203.
Pueyo, E.L., et al. (1995). Determining emplacement mechanisms of granitoids: application of structural and magnetic methods (ASM & IRM zoning). Journal of Czech Geological Society, 40(3), 72.
Pueyo, E.L., et al. (2022). Petrophysical Characterization of Non-Magnetic Granites; Density and Magnetic Susceptibility Relationships. Geosciences, 12(6), 240.
Rochette, P. (1987). Magnetic susceptibility of the rock matrix related to magnetic fabric studies. Journal of Structural Geology, 9(8), 1015-1020.
Rochette, P., Jackson, M., & Aubourg, C. (1992). Rock magnetism and the interpretation of anisotropy of magnetic susceptibility. Reviews of Geophysics, 30(3), 209-226.
Román-Berdiel, T., et al., (1995). Granite emplacement during contemporary shortening and normal faulting: structural and magnetic study of the Veiga Massif (NW Spain). Journal of Structural Geology, 17(12), 1689-1706.
Román-Berdiel, T., et al., (1998). Compressional granite-emplacement model: structural and magnetic study of the Trives Massif (NW Spain). Lithos, 44(1-2), 37-52.
Román-Berdiel, T., et al. (2004). The main Variscan deformation event in the Pyrenees: new data from the structural study of the Bielsa granite. Journal of Structural Geology, 26(4), 659-677.
Román-Berdiel, T., et al. (2006). The Variscan Millares granite (central Pyrenees): Pluton emplacement in a T fracture of a dextral shear zone. Geodinamica Acta, 19(3-4), 197-211.
Sant'Ovaia, H., et al. (2000). Composite-laccolith emplacement of the post-tectonic Vila Pouca de Aguiar granite pluton (northern Portugal): a combined AMS and gravity study. Earth and Environmental Science Transactions of The Royal Society of Edinburgh, 91(1-2), 123-137.
Sant’Ovaia, H., et al. (2010). Magmatic structures and kinematics emplacement of the Variscan granites from Central Portugal (Serra da Estrela and Castro Daire areas). Journal of Structural Geology, 32(10), 1450-1465.
Terrinha, P., et al. (2018). Gravimetric and magnetic fabric study of the Sintra Igneous complex: laccolith-plug emplacement in the Western Iberian passive margin. International Journal of Earth Sciences, 107(5), 1807-1833.
Comments for author File: Comments.pdf
Author Response
Dear Reviewer,
Thank you very much for your comments. In the attached document, we explain what we have done.
Best regards,
Cláudia.
Author Response File: Author Response.pdf
Reviewer 3 Report
Minor comments:
Line 83: Please provide references for the formulas.
Line 98: Please give details about the method used to measure AMS using KLYF5: manual, classic rotator, or 3D rotator. What type of specimen: cylinder or cube? Dimensions?
Major comment:
Line 198-199: The presence of SP grains is an essential fact in the interpretation of the measurements. Do you have independent measurements (e.g. frequency dependence of magnetic susceptibility) to support a significant presence of SP particles? Please comment on this aspect in the text.
Author Response
Dear Reviewer,
Thank you very much for your comments. In the attached document, we explain what we have done.
Best regards,
Cláudia.
Author Response File: Author Response.pdf
