|The revised version is clearly an improvement and the authors have addressed many of the two reviewers’ comments. The paper can, in my opinion, go in the press with some minor modification, although I am still not convinced by the interpretations of the tomographic images. The final geodynamic interpretation in terms of subduction polarity is logical given the interpretations of seismological data and also given the surface geology. Despite my disagreements I think that the publication of this paper can foster some useful debates.|
One of the main improvements is that the notion of a “tectosphere” has disappeared in the new version. It was clearly not different from what we usually call “lithosphere” and its use was blurring the main message. By the way, I would like to stress the fact that Elsasser (1969) indeed used the term tectosphere and even showed figures stressing that it meant a rigid lid moving coherently above a weaker asthenosphere, in contradiction with the authors’s reply to one of my comments. The paper corresponds to a chapter in a book edited by Runcorn. The reference is:
Elsasser, W. M.: Convection and stress propagation in the lower mantle, in: The application of modern physics to the Earth and planetary interiors, edited by: Runcorn, W. K., Interscience, New York, 223-246, 1969.
Otherwise, I am still puzzled by the interpretation of the thickness of the European lithosphere. The main argument used in the paper is that the tomographic profiles show a package of coherent anomalies dipping toward the internal zones and the base of this package (i.e. below the low velocity anomaly) should be the base of the lithosphere (see figures 3C or 7B for instance). I can indeed see this “package” but I do not see any information telling us where the base of the lithosphere is. It is said page 13, lines 406-407, that this positive-negative anomaly layering makes up a “coherent kinematic entity”. The profile does not show any kinematic information and I cannot clearly see what in the seismological information tells that the base of the lithosphere should be placed there. I have nothing a priori against the idead- that the European lithosphere is thicker than usually thought, but if I look at the tomographic data alone, I do not see it. It seems that you have decided a priori that it should be there or, else, I totally missed your reasoning.
Chapter 4 (choice of the interpretation of seismic structure) should in my opinion come before you actually describe your interpretation, which is presently done in chapter 3. It would not change the conclusions but it would be more logical.
In the regional tectonic interpretation (from line 474) you mention that you marked boundaries (thick black lines) around “kinematically coherent images”. Once more, what does tomography tell us about kinematics ?
Lines 848-849: you suggest that “the Vp layer in the European lithosphere is structurally anisotropic and may have accommodated viscous flow”. Is it still the lithosphere then ?
Lines 857 and following: the European lithosphere is not as old as you say. After the Permian thermal overprint it was also affected by the Triassic rifting and then the Liassic rifting event.
Figure 11: this nice sketch is not in agreement with your conclusions as the European lithospheric lid is not thicker than 100km, instead of 200.
Line 17: please change “anomalously” to “anomalously”. Check throughout manuscript, the same misspelling occurs at least one more time.
Line 576: “Becculava” is probably “Beccaluva”, please check.