Dear authors, reviewers and editors,

As I recently worked on exactly the same topic as some parts of the present paper, namely the rift architecture and synthesis of geological history of the Afar Region (Rime et al., 2023), I hope I can bring some useful comment on this manuscript.

One important focus of the present paper is the discussion of the influence of plume on rifting (in particular triple junctions) and vice and versa (active vs. passive rifting). I think that the scenario of plume-induced rotation is interesting and plausible, but I will focus my comments on the structure and history of the Afar Region as my expertise rather lies in this part.

One of the pitfalls of this manuscript is the lack of consideration of geological data and overreliance and overinterpretation of geophysical data. For the onshore part of the Region, many geological data are available (see reference list in Rime et al., 2023) but have been overlooked in this manuscript.

This is mainly seen in fig. 11 which maps “axial segments” with black lines. As the term “axial segments” has not been defined, I’m not 100% sure what was meant, but I assume it is roughly similar to what we name “rift segment” in our paper, i.e. continuous strain accommodating areas testified by faulting and, in some cases, magmatic activity and/or formation of sedimentary basin. In our paper, we have studied the structure of the Afar Region with the same methods as this manuscript (topography, seismicity, BGA and VGG), but we have combined them with lots of surface geological data from several hundreds of references, and we came out with quite different results.

The lines represented on fig. 11 in fact represent geophysical lineations that do not necessarily represent an axial segment. Geophysical lineaments are good tools in the absence of access to the geology (e.g. Augustin et al., 2021) but in this complex area, the surface or near-surface geology, as well as other geological data need to be taken into account.

I attached a version of this figure with colours and number to be able to discuss individual mapped axial segments:

1. This axial segment is cross-cutting magnetic anomalies (Fournier et al., 2010) and it is barely plausible to have an axial segment cross-cutting oceanic crust there. It was apparently traced based on BGA data (fig. 8) but on the same figure (taking into account the obliquity of extension), you see an almost perfect symmetry between both side of the MOR on all dataset (topography, VGG and BGA), I thus don’t see why it is interpreted as an axial segment.
2. This axial segment was mapped based on VGG (fig. 10) but only represent a limit between the sediment-filled Western Guban Basin and the Ali Sabieh Block, with occurrence of shallow basement and volcanic cover (Le Gall et al., 2015; Ali, 2015; Rime et al., 2022b, 2022a, 2023). It therefore does not represent an axial segment but a boundary between two geological regions with different characteristics.
3. Idem but for the western margin of the Ali Sabieh Block. It just represents the limit between shallow basement with relatively thin volcanic cover on the Ali Sabieh Block and deep, massively intruded basement and thick volcanic cover in the Depression sensu stricto.
4. This line (we don’t know from which data it is interpreted) is incompatible with surface data. It cross-cut all structures visible on the surface that are active since the Pliocene (look at fault pattern on our map (Rime et al., 2022a) or any other map of the Depression or just Google Earth).
5. This line was mapped based on VGG data (fig. 10) but this lineament just represents the combination of a topographic low and the presence of a low-density sedimentary basin. The axial segments in the southern Danakil Depression are marked by the volcanic ranges and not by the sedimentary basins (Barberi et al., 1970, 1972; Barberi and Varet, 1970; Tazieff et al., 1972; Le Gall et al., 2018; Watts et al., 2020; Schaegis et al., 2021; Rime et al., 2023).
6. This axial segment is not curved. It represents two different overlapping segments (the Erta Ale and the Tat’Ali segments in our publication) but both are straights. In the north, the rift axis continues straight into the salt plain (Bastow et al., 2018; Schaegis et al., 2021; Hurman et al., 2023; Rime et al., 2023). Further north, there is indeed a puzzling link between the Danakil Depression and the Howlakil Bay visible on BGA data but surface geology and other geophysical data strongly suggests that the axial segment continues towards the Gulf of Zula until jumping west of the Mt. Ghedem (Viltres et al., 2020; Ruch et al., 2021; Rime et al., 2023).
7. This line connects several different geological features but does not represent a continuous axial segment. The southernmost part of the line represents Teru Graben (which we classify as a rift segment) but then it jumps to the western sedimentary basin of the Erta Ale (like for comment on line 5, this is not an axial segment) before finally jumping to the sedimentary basin forming the rift axis in the northern part of the Danakil Depression.

These are the main problems I see on this figure, but other lines are also questionable, and some axial segments presented in the literature could be added (Hammond et al., 2011; Rime et al., 2023).

Comments on Section 7.2: Spatial constraints in the development of the plume-rift system:

While initially presented as spatial constraints, the two tectonic events described (MER connection with the Gulf of Aden / Red Sea system and the abandonment of the Bab-el-Mandeb segment) are then suddenly considered in line 424 (and lines 402-404 indirectly) as a temporal constrain where the former happens after the latter. There is no argumentation in the text for this change between two spatially separated tectonic events and two temporally separated events. We have discussed these events in our paper (section 6) and, based on numerous geological constrains, we show that they happen roughly at the same time. If your interpretation is different, it should be explained.

I also see confusion regarding margin curvature. For a margin to be curved clockwise or counterclockwise, you have to define a direction in which you observe it. E.g., the somalian margin is curved clockwise if considered from E to W but counterclockwise if considered from W to E. As such, the comparison between margin curvature and block rotation is sketchy. I don’t believe that the curvature of the Ethiopian margin (if you mean the curvature between approx. 9°N and 14°N) is linked with the rotation of the Danakil Block but rather with the linkage between the MER and the Gulf of Aden / Red Sea / Afar Rift System.

Other comments:

• Line 251-254: Not completely true. You find pre-rift trap basalts in the Depression and Late Miocene and younger (so syn-rift) lavas on the plateaus (e.g. Rime et al., 2022).
• Lines 340-341: Keep also in mind that there is a microcontinent in between: the Arrata or Danakil Microplate and that the rotation of this microplate is the reason why the structure are not all aligned (Zwaan et al., 2020).
• Lines 341-352: This is why we propose that the Red Sea Rift and Afar Rift are distinct. See discussion on the topic with references to the literature in section 5 of our paper.
• Line 363-365: They are many papers discussing this, and it’s probably not bad to cite a few more (Tazieff et al., 1972; Barberi and Varet, 1977; Acton et al., 1991; Manighetti et al., 2001; Eagles et al., 2002; Audin et al., 2004; Kogan et al., 2012; Pagli et al., 2014; Doubre et al., 2017; Moore et al., 2021; Rime et al., 2023).
• On northward propagation of the MER: this a controversial issue and the literature is not conclusive. See section 5.2.1 of our paper for reference list on the topic.
• The conclusion that the Afar does not conform to a typical R-R-R triple junction with rift propagating away from the triple junction was already discussed in several papers (Mohr, 1970, 1972; Girdler, 1991; Manighetti et al., 1997; Hébert et al., 2001; Wolfenden et al., 2004; Purcell, 2018; Khalil et al., 2020; Maestrelli et al., 2022; Rime et al., 2023). It’s probably not bad to mention it.
• It is mentioned several times in the manuscript that the margins of the MER are smooth, continuous and the axial ranges are parallel to the margins (e.g. line 330-331). This is only partly true. The volcanic segments of the MER are en-échellon compared to the margins and thus not completely continuous and parallel (see Corti, 2009 and numerous publications by this author).
• Line 396: Numerous evidence suggest that this rotation started around 10 Ma ago (Eagles et al., 2002; McClusky et al., 2010; Reilinger and McClusky, 2011; Rime et al., 2023).
• Line 393: The authors of the mentioned paper say that “the channel most likely does not have a tectonic origin”. The most likely explanation is a massive inflow event. If a hypothetical graben would be active now, it would contradict your idea that this connection is inactive. If it was inactive since the Late Miocene, there was plenty of time (and sediments) to fill it. However, I don’t discuss the fact that the Mab-el-Mandeb is an abandoned rift segment. See also the geological evidence from other references cited in our paper (sections 4.3.1 and 4.6).
• Figure 1: It’s strange to have a lot of emerged land coloured in blue.
• Figure 3: The Shurka el Sheik Discontinuity is not indicated in the correct place. It should be further W (like on fig. 6).

Overall, I think that the manuscript should be at least corrected regarding the position of the axial segments and some interpretation toned down, removed or better justified, in particular for the temporal relationship between the two events described in section 7.2. Finally, a more thorough literature review would have been useful. Several points raised and discussed in this manuscript were already discussed in the literature since decades and these studies should be mentioned.

Best regards,

Valentin Rime

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