Assessing the Magnetic Mineralogy of the Pre-Variscan Manteigas Granodiorite: An Unexpected Case of a Magnetite-Series Granitoid in Portugal

Round 1

Reviewer 1 Report

My major concern about this work is that readers can confuse the studied granodiorite massif with another Variscan pluton while it is classified as an old Early Ordovician pluton forming part of a small amphibole- and/or biotite-bearing granitoid (tonalite to granite) composite plutonic belt. I think that this pre-Variscan batholith is currently well defined after several works dealing with U-Pb geochronological dating of these old granite massifs (e.g., Solá et al., 2008; Neiva et al., 2009; Antunes et al., 2009; Rubio-Ordóñez et al., 2012; Pereira et al., 2018; Crispim et al., 2022). Most of these authors suggest an I-type (or I- transitional to S-type) feature for tonalite and granodiorite units, although fractionated types are usually peraluminous. More debatable is their geodynamic setting, but it tends to be related to some kind of magmatic arc or subduction zone in a continental plate edge (e.g., Rubio-Ordóñez et al., 2012, and references therein; Pereira et al., 2018). So, I suggest to introduce this question of the pre-Variscan age of the Manteigas granodiorite massif in the Title, Abstract and Geological Setting sections. Otherwise, this does not change the validity and relevance of the work.

 

Geological Setting section needs some reorganization. See below:

Line 100 - I miss a paragraph explaining the presence of that small array of Early Ordovician plutons along the southern area of the Central Iberian Zone (see e.g., Antunes et al., 2009; Rubio-Ordóñez et al., 2012). This has to include a short summary of geochemical features (e.g., I-S transitional type characteristics), age (mostly from 478 to 486 Ma, Manteigas pluton of Neiva et al., 2009; Oledo pluton of Antunes et al., 2009; Zarza la Mayor pluton of Rubio-Ordóñez et al., 2012; Batao tonalite of Crispim et al., 2022) and its supposed geodynamic setting that could be close to a plate edge (e.g., Rubio Ordóñez et al, 2012; Pereira et al., 2018).

122 - Please, add at the end of the sentence: “and also to the studied pre-Variscan Manteigas massif”.

129 – Please add (after Seia granite) “of late-D3 Variscan age”.

Lines 142 to 151 – I suggest to move this discussion to line 100, but I think that U-Pb zircon data from Neiva et al. (2009) is enough evidence, against age-deduced means by cartographical features, made by older references [27, 30,34,35], that Manteiga granodiorite is a pre-Variscan intrusion.

 

Petrography section (lines 204 to 220) needs to reword mineral description to present times (e.g., quartz “shows” instead of “showed”) in some sentences.

 

Conclusions section needs some rewriting (see also annotated ms):

Line 377 - I suggest to introduce a short line in the sense of “No previous studies on pre-Variscan granites of the same Central Iberian Zone were undertaken” In this sense, a previous work [24] showed ….. 

412 – Rewrite sentence: magnetite crystals with a size of ca. 2 μ in amounts of around 0.01 vol%.

415-6: Alternative redaction: this ferrimagnetic mineral may be present in small grains and at low concentrations, when it is partially oxidized to hematite (martite pseudomorphism).

 

In reference list some numbers (17, 18 and 42, 43) have been left out. References 1, 3, 12, 21, 24, 41 and 47 miss some data (e.g., journal, volume number, pages...). Reference 29 is bizarre and it seems there is some problems with reference number 38.

 

 

References added in the review:

Antunes, I.M.H.R., Neiva, A.M.R., Silva, M.M.V.G., Corfu, F. (2009) The genesis of I- and S-type granitoid rocks of the Early Ordovician Oledo pluton, Central Iberian Zone (central Portugal). Lithos 111, 168-185.

Crispim, L., Chichorro, M., Bento dos Santos, T.M., Linneman, U., Hofmann, M., Neto de Carvalho, C. (2022) U-Pb zircon geochronology of metasedimentary and igneous rocks from Penha Garcia-Salvaterra do Extremo sector, Central Iberian Zone. In Ossa-Morena and beyond: a tribute to Teodoro Palacios (S. Jensen, ed) Abstract Book, 9-10.

Pereira, M.F., Castro, A., Fernández, C., Rodríguez, C. (2018). Multiple Paleozoic magmatic-orogenic events in the Central Extremadura batholith (Iberian Variscan Belt, Spain). Journal of Iberian Geology 44, 309-333.

Rubio-Ordóñez, A., Valverde-Vaquero, P., Corretgé, L.G., Cuesta-Fernández, A., Gallastegui, G., Fernández- González, M., Gerdes, A. (2012). An Early Ordovician tonalitic-granodioritic belt along the Schistose-Greywacke Domain of the Central Iberian Zone (Iberian Massif, Variscan Belt). Geological Magazine 149, 927-939.

Solá, A.R., Pereira, M.F., Williams, I.S., Ribeiro, M.L., Neiva, A.M.R., Montero, P., Bea, F., Zinger, T. (2008) New insights from U-Pb zircon dating of Early Orodovician magmatism on the northern Gondwana margin: The Urra Formation (SW Iberian Massif, Portugal). Tectonophysics 461, 114-129.

 

 

 

Madrid April 2022

Carlos Villaseca

Comments for author File: Comments.pdf

Author Response

Dear Carlos Villaseca,

Thank you very much for your comments. In the attached table we explain what we have done.

Best regards

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript presents a problem of the occurrence of minerals with magnetic properties (mainly, but not only magnetite) in granitoid and the resulting possible suggestions on the parent magma source and some aspects of the formed rock evolution. The reconstruction of the magmatic rock origin process is not a trivial problem and any properly made study with correctly obtained conclusions is worthy publishing. The reviewed manuscript is just of this kind.

However, the text needs some improvements. First, as it is now trendy, the title is too long – for instance I do not understand the use of the wording “unexpected case”; if the study resulted in an expected data, probably the publishing of them would not be reasonable.

The authors commonly use “toto pro partes”: mineralogy instead mineralogical composition, mineralogical studies etc.; this also concerns “petrography”, “methodology” and so on. This style makes an impression of a jargon. Moreover, such very strange (and senseless) expressions are used: magnetic mineralogy, magnetite-type granitoid and other ones. The scientific text should be precise.

Some grammatical errors (unfortunately, common ones in the scientific texts) were found, e.g. “based on” or joining of passive voice with present participle (an example: were made using).

At few places the text is not clear.

The detailed remarks are added to the text as sticky notes.

After the indicated corrections I would suggest publication of this article.

Comments for author File: Comments.pdf

Author Response

Dear Anonymous Reviewer,

Thank you very much for your comments. In the attached table, we explain what we have done.

Best regards!

Author Response File: Author Response.pdf