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    Review of 'Tectono-stratigraphic correlations between Northern Evvoia, Skopelos and Alonnisos, and the postulated collision of the Pelagonian carbonate platform with the Paikon forearc basin (Pelagonian-Vardar zones, Internal Hellenides)'

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    Tectono-stratigraphic correlations between Northern Evvoia, Skopelos and Alonnisos, and the postulated collision of the Pelagonian carbonate platform with the Paikon forearc basin (Pelagonian-Vardar zones, Internal Hellenides)Crossref
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    Tectono-stratigraphic correlations between Northern Evvoia, Skopelos and Alonnisos, and the postulated collision of the Pelagonian carbonate platform with the Paikon forearc basin (Pelagonian-Vardar zones, Internal Hellenides)

     Rudolph Scherreiks,  Marcelle Boudagher-Fadel (corresponding) (2019)
    The Pelagonian stratigraphy of the study area consists of a Permo-Triassic basement and an Upper Triassic and Jurassic carbonate platform formation that had been overthrust by the Eohellenic ophiolite sheet during the Early Cretaceous. Intensive erosion, during the Cretaceous, removed most of the ophiolite and partly the Jurassic formation. It is hypothesised that uplift and erosion of eastern Pelagonia had been triggered by the break-off of the subducted oceanic leading edge of the Pelagonian plate. An investigation of the rocks that succeed the erosional unconformity shows that they constitute a shear-zone-formation which is tectonically overlain by Cretaceous platform carbonates that characterise the Palouki series of Skopelos and Alonnisos. Geochemical analyses of the shear-zone rocks substantiate that they are of mid ocean ridge and island arc provenience. Eastern Pelagonia collided with a Cretaceous carbonate platform, probably the Paikon-Paeonian forearc basin, as the Almopias ocean subducted beneath that island-arc-complex. The Cretaceous platform, together with a substrate of sheared-off ocean floor mélange, overthrust eastern Pelagonia as subduction continued, and the substrate was dynamically metamorphosed to cataclastic rocks, mylonite, phyllonite and interpreted pseudotachylite. This complex of Cretaceous platform rocks and a brittle-ductile shear-zone-substrate constitute the here named Paikon-Palouki nappe which was emplaced during Early Palaeocene. The Paikon-Palouki nappe did not reach Evvoia. Seismic tomographic models of the Aegean region apparently depict images of two broken-off ocean-plate-slabs, interpreted as Almopias-lithosphere-slabs: the western Almopias slab began to sink during the Early Cretaceous, the eastern Almopias slab broke off and sank after the Paikon-Palouki nappe was emplaced in Early Palaeocene time.
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      Review information

      10.14293/S2199-1006.1.SOR-GEO.AQRUNF.v1.RNMPBQ

      This work has been published open access under Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com.

      Keywords:

      Review text

      Review: Tectono-stratigraphic correlations between Northern Evvoia, Skopelos and Alonnisos, and the postulated collision of the Pelagonian carbonate platform with the Paikon forearc basin (Pelagonian-Vardar zones, Internal Hellenides)

      The manuscript presents important new fieldwork mainly on the islands Skopelos and Alonnisos and reviews the available literature for the tectonic model and stratigraphy. Oceanic crust rocks on the islands of Alonnisos and Skopelos have been reinterpreted to be part of a large shear zone that extends over the islands of the northern Sporades. The paper also reinterprets basement rocks on Skopelos as Triassic similar to Evvoia. The main conclusion is that the Cretaceous carbonate platform (Paikon-Palouki Nappe) was thrusted over the old basement and is not in sedimentary contact. This has implications for the tectonic history and the paleogeography, and new ideas are presented to explain the observed findings. I consider the work presented as very valuable, showing the importance of new fieldwork and analytical work. The stratigraphy of the islands is controversial in the literature with various different interpretations that are well summarised in the manuscript, which enables the reader to follow critical new interpretations.

      However, I have a few points I would like to raise in this review. Punctuation and English sentence structure need a further proof read. I have suggested some changes for the authors to consider. I also would suggest that the authors add more context and background so that the reader can better follow the steps from the results presented, to the interpretation, and then to the conclusions. The manuscript also would benefit from a better organisation. At present some conclusions are already anticipated in earlier parts of the manuscript.

      Introduction

      Page 1: Basement in Glossa. It would be useful to modify Fig. 1b to give more attention to the basement in Glossa and its correlation with Evvoia.

      Please help the reader in the Introduction what the study will be about and why. Without going into interpretation or conclusions.

      Style of indention for new paragraph sections is not consistent. Most have an indent but, for example, the Geological background (please correct to lower case) section has not.

      Geological Background and previous research

      The section geological background could be expanded to present a better introduction of the Vardar zone and the tectonic history of the region, so that an audience not familiar with the current subduction model of Pelagonia and the Almopias ocean could better follow the text. For this section, a paleogeography map might help.

      Page 2 last section on background: please move the brackets and change to (see Discussion-Pelagonian Basement) before the comma and delete the point after the brackets.

      Disputed and modified stratigraphies of Alonnisos and Skopelos

      Page 2 last section: add the b figure to …previous stratigraphies are compared to the new stratigraphy (Fig. 3a and b).

      Page 3 line 14: ‘The conglomerate contains…’

      Page 3 line 15: please add ‘and is in turn overlain by…’

      Page 3: the laterite deposits are not in the stratigraphy Figure 3a. If the laterites are interpreted to be a product of metabasite alteration, it has to be stated.

      The Paikon-Palouki nappe and the brittle-ductile shear-zone formation

      It would help the reader to first establish what the Paikon-Palouki nappe is… e.g. Cretaceous carbonate platform, and not at the end of the paragraph. If the previous recognised Palouki nappe is introduced, it has to be explained what this is.

      Page 3 line 36: please add the numerical age of the new Ar data for the reader.

      Porkoláb et al. (2019) dated micas in the shear zone. Why would the micas in the shear zone give an age for deformation in the overlying nappe? Please expand to explain that the shear zone formation occurred during thrusting after deposition of the Cretaceous carbonate. Or was the nappe later thrusted over the shear zone? Also, it hasn’t been established in the manuscript that the nappe is deformed.

      Page 3 please change to: …rocks on Alonnisos and Skopelos have previously been observed, including…and/or were interpreted as…

      Page 3 please change to: A greenschist of Kira Panagia has been interpreted as a metabasite or as arc-tholeiite basalt-rhyodacite…

      The Brittle-Ductile Shear-Zone Formation

      Page 4: it is implied that the shear zone grades into the Cretaceous carbonate. Please clarify what the structural contact is. Is the carbonate part of the shear zone, or does it overlie it with a fault contact?

      Page 4 line 26: insert brackets for Higgins reference.

      Description of the geologic maps and cross sections of Alonnisos and Skopelos

      Geology and tectonic sections of Alonnisos

      Please remind the reader what the Eohellenic nappe is, that had been removed.

      Page 4 please change: Our new geological map of Alonnisos mainly differs in two areas from the previous map(s)…

      I assume the two areas are the disputed areas marked red on the map. If so please refer to those in the text. It would also help to state what was corrected in these areas.

      The next two sentences which start with Frank (1997) need to be rewritten. What is the Mourtero series that is referred to here? Please explain. Why is this series in the mapping section of Alonnisos especially named, but no other stratigraphic unit discussed?

      Please move the Skopelos map sentence to the Skopelos section below.

      The Pelagonian basement of Skopelos

      Page 4: Please give context to what the two series are (at present the reader has to look into the figure).

      Page 5 please add: “Eohellenic ophiolite outliers on Alonnisos”

      Page 5 typo:  ‘occurred’

      Page 5 typo: Early Cretaceous

      Page 5 line 11 typo: spelling of Porkoláb et al. (2019).

      Page 5: please mark the important thrust fault on the map more clearly.

      Description of the tectonic sections

      Page 5: Barker reference in blue

      Page 5: What are the Vardar formations?

      The allochthonous Cretaceous and subjacent shear zone

      Page 5: remove brackets around the reference name

      Biostratigraphy

      Please help the reader in adding formation or series names to the analysed microfossils and consider reordering from old to young. It could follow a short summary showing which formation has which age.

      Page 6: Cladocoropsis (in italics) finding.

      Page 6: Matarangas (1992) reported Actinoporella podolica Alth in…

      Please add sentence end point after (BouDagher-Fadel 2008, 2015).

      Radiolitidae and Hippuritidae in italics

      Geochemistry of the shear zone formation

      Page 7 line 10, please add: and (before the mineral grains of plg)

      Fig. 4b: please change the symbol for Glossa or the shear-zone metabasites (hard to differentiate)

      Please clarify: …mostly of a MORB origin but many indicating IAB provenance (a few indicate IAB?)

      Discussion

      The shear zone formation

      phyllic alteration (lower case)

      The geotectonic evolution of the study area

      A paleogeography map (not just the cross section presented) would help the reader to understand where the carbonate platform was formed.

      Subductions of two slabs of oceanic lithosphere

      What was the original interpretation of Bijwaard et al. and Hafkenscheid for the two anomalies?

      As far as I understand the figures X was an earlier subduction phase (or contemporaneous to Y), but did the slab break-off and subduction cease while Y was still subducting? If so, I would like to ask the authors to add a few sentences to better explain their model for an audience that might not be too familiar with the subduction history of the area.

      Page 10 line 5: bracket before Fieldwork is not closed.

       

      Tim Breitfeld

      Comments

      Dear Tim

      Thank you so much for reviewing our paper. We have taken into accounts all of the points you suggested. They are all valid and helpful, and have been addressed and revised in the text.

      Best wishes

      Marcelle and Rudolph  

      2020-02-21 13:19 UTC
      +1

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