The impact of rotational rifting on the evolution of the East African Rift System: an analogue modelling study

Zwaan, Frank; Schreurs, Guido

doi:https://doi.org/10.5194/egusphere-2022-1365

Preprints

https://doi.org/10.5194/egusphere-2022-1365

Preprints

02 Jan 2023

| 02 Jan 2023

The impact of rotational rifting on the evolution of the East African Rift System: an analogue modelling study

Frank Zwaan and Guido Schreurs

Abstract. The East African Rift System (EARS) represents a major tectonic feature splitting the African continent apart into the Nubian Plate situated to the west, and the Somalian Plate to the east. The EARS comprises various rift segments and two microplates (the Victoria and Rovuma plates) and represents a key location for studying rift evolution. Researchers have proposed various scenarios for the evolution of the EARS, but the impact of continental-scale rotational rifting, caused by the rotation of the Somalian Plate, has received only limited attention. In this study we apply analogue models to explore the dynamic evolution of the EARS within the broader rotational rifting framework. Our models show that rotational rifting leads to the lateral propagation of deformation towards the rotation axis, but we must distinguish between the propagation of distributed deformation, which can move very rapidly, and localized deformation, which can significantly lag behind. The various structural weakness arrangements in our models (representing pre-existing structural heterogeneities) lead to a variety of different structures. Laterally overlapping weaknesses are required for localizing parallel rift basins to create rift pass structures, possibly leading to the rotation and segregation of micro-plates, as is the case for the Victoria Plate in the EARS. Additional model observations concern the development of early pairs of rift-bounding faults flanking the rift basins, followed by the localization of deformation along the axes of the most advanced rift basins. Furthermore, the orientation of rift segments with respect to the regional (rotational) plate divergence affects deformation along these segments: oblique rift segments are less wide due to a strike-slip deformation component. Overall, our model results are a good fit with the large-scale features of the EARS, providing constraints on the timing of rift development and on the segregation and rotation of the Victoria plate within the broader rotational rifting framework of the EARS.

Received: 30 Nov 2022 – Discussion started: 02 Jan 2023

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Journal article(s) based on this preprint

07 Aug 2023

The link between Somalian Plate rotation and the East African Rift System: an analogue modelling study

Frank Zwaan and Guido Schreurs

Solid Earth, 14, 823–845, https://doi.org/10.5194/se-14-823-2023,https://doi.org/10.5194/se-14-823-2023, 2023

Short summary

Frank Zwaan and Guido Schreurs

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2022-1365', Cynthia Ebinger, 06 Feb 2023
Zwaan and Schreurs utilize fully scaled analogue models to investigate the role of rotational stresses on the continental-scale spatial evolution of rift zones, with comparison to rifting patterns in East Africa. The models explore a range of co-eval rift initiation geometries, and then track the time evolution of strain for comparison with the modern geometry of active rift zones in parts of E Africa. The models ignore rifting in the offshore SE rift branch in oceanic lithosphere east and southeast of the Rovuma block, and the SW branch that continues perhaps as far west as Angola around the San block.

My major concern with the paper is the reliance on outdated structural models based on coarse satellite imagery, and lacking information from seismicity and geodesy that shows modern plate motions. Specifically, the papers cited for the role of pre-existing basement shear zones are all based on satellite imagery and lack the 3^rd dimension – the dip of structures. Likewise, the age of some lineaments mapped in these publications remains speculative (e.g., Chorowicz, 2005), and papers utilizing displacement of data strata should only be considered.

The comparisons with data in Section 4.15 as well as model constraints need to be re-thought, and omission of processes (e.g., magmatism, GPE, etc) need to be clearly articulated.

Seismicity (Lindenfeld, M., Rümpker, G., Link, K., Koehn, D., & Batte, A. (2012). Fluid-triggered earthquake swarms in the Rwenzori region, East African Rift—Evidence for rift initiation. Tectonophysics, 566, 95-104; Lavayssière, A., Drooff, C., Ebinger, C., Gallacher, R., Illsley‐Kemp, F., Oliva, S. J., & Keir, D. (2019). Depth extent and kinematics of faulting in the southern Tanganyika rift, Africa. Tectonics, 38(3), 842-862; Ebinger, C. J., Oliva, S. J., Pham, T. Q., Peterson, K., Chindandali, P., Illsley‐Kemp, F., ... & Mulibo, G. (2019). Kinematics of active deformation in the Malawi rift and Rungwe Volcanic Province, Africa. Geochemistry, Geophysics, Geosystems, 20(8), 3928-3951; Weinstein, A., Oliva, S. J., Ebinger, C. J., Roecker, S., Tiberi, C., Aman, M., ... & Fischer, T. P. (2017). Fault‐magma interactions during early continental rifting: Seismicity of the M agadi‐N atron‐M anyara basins, A frica. Geochemistry, Geophysics, Geosystems, 18(10), 3662-3686; Zheng, W., Oliva, S. J., Ebinger, C., & Pritchard, M. E. (2020). Aseismic deformation during the 2014 M w 5.2 Karonga earthquake, Malawi, from satellite interferometry and earthquake source mechanisms. Geophysical Research Letters, 47(22), e2020GL090930) and geodetic strain from active plate motion and time-averaged strains (e.g., DeMets, C., & Merkouriev, S. (2021). Detailed reconstructions of India–Somalia Plate motion, 60 Ma to present: implications for Somalia Plate absolute motion and India–Eurasia Plate motion. Geophysical Journal International, 227(3), 1730-1767; Stamps, D. S., Kreemer, C., Fernandes, R., Rajaonarison, T. A., & Rambolamanana, G. (2021). Redefining east African rift system kinematics. Geology, 49(2), 150-155; Knappe, E., Bendick, R., Ebinger, C., Birhanu, Y., Lewi, E., Floyd, M., ... & Perry, M. (2020). Accommodation of East African rifting across the Turkana depression. Journal of Geophysical Research: Solid Earth, 125(2), e2019JB018469; Birhanu, Y., Bendick, R., Fisseha, S., Lewi, E., Floyd, M., King, R., & Reilinger, R. (2016). GPS constraints on broad scale extension in the Ethiopian Highlands and Main Ethiopian Rift. Geophysical Research Letters, 43(13), 6844-6851; Viltres, R., Jónsson, S., Ruch, J., Doubre, C., Reilinger, R., Floyd, M., & Ogubazghi, G. (2020). Kinematics and deformation of the southern Red Sea region from GPS observations. Geophysical Journal International, 221(3), 2143-2154.)

The authors cite decades-old papers to quote a N to S younging, inferring a N-S propagation of rifting throughout the EAR. Yet, the only two sectors of the EAR confirming that pattern are the Eastern rift in Kenya and N Tanzania, and the southern Malawi rift. The MER appears to have propagated from S to N, and the very poorly date Western rift may have initiated near the Rungwe volcanic province, and propagated both N and S from there (e.g., Roberts, E. M., Stevens, N. J., O’Connor, P. M., Dirks, P. H. G. M., Gottfried, M. D., Clyde, W. C., ... & Hemming, S. (2012). Initiation of the western branch of the East African Rift coeval with the eastern branch. Nature Geoscience, 5(4), 289-294.). See also Daly MC, Green P, Watts AB, Davies O, Chibesakunda F, and Walker R (2020) Tectonics and Landscape of the Central African Plateau, and their implications for a propagating
Southwestern Rift in Africa. Geochemistry, Geophysics, Geosystems. e2019GC008746. For information on the SW rift zone.

Other major concerns are as follows:

The EAR formed above one or more mantle plumes, and topographic relief within the region is > 1000 km. How do the authors include GPE? If not, tell the reader that it is ignored.

Likewise, parts of the study area have experienced 2+ km of magmatic underplate and have strain accommodated by magma intrusion. Since this is not included, tell the reader and consider the consequences.

Parts of the study area are underlain by cratonic roots that are 70 km thicker than surrounding areas. Since this is not considered, tell the reader and consider the consequences.

On what basis did the authors choose these models? Without careful consideration of the timing of diachronous rifting data, choice of models could be biased to outdated and inaccurate information.

Minor comments

Segments is generally used to describe a single fault-defined basin unit, whose length depends on the strength of the plate.

Line 48 - Strike slip faulting happens in accommodation zones and may reactivate a variety of basement sttructures, but overall, the rift structures form irrespective of basement structures. Please don't list my name there.

Line 53: What do you mean by an inherited weakness? THe 'weaknesses' are highly variable in the cited papers. What about the role of variable rheology linked to plate thickness (and hence geothermal gradient), composition, pre-existing thin zones, availability of melt, not just shear zones: see Muirhead et al., 2020;

Summary

The authors have published earlier papers considering rift models, which is in part why I urge them to dig more deeply into assumptions, and to move beyond EAR mythology to factual data constraining modern plate boundary deformation, and to move past lineament analyses.
Citation: https://doi.org/10.5194/egusphere-2022-1365-RC1
- AC2: 'Reply on RC1', Frank Zwaan, 29 Mar 2023
  
  We kindly thank the reviewer for the detailed assessment of our manuscript, and have addressed the comments in the PDF file we uploaded.
  
  Citation: https://doi.org/10.5194/egusphere-2022-1365-AC2
RC2:
'Comment on egusphere-2022-1365', Georgios-Pavlos Farangitakis, 11 Feb 2023
The authors present a novel analogue modelling approach through a rotating apparatus to delineate the evolution in response to rotational motions of rifts and use the East African Rift System as a natural example. They explore different rift-seed configurations and how these reflect on various features of the East African Rift System, making observations in the process about rotational stresses, microplate formation and preferential rift (re)activation.
A particularly novel part of this work is that the authors do a direct comparison on the initiation of a rift based on top-view photos, digital topography and particle tracing techniques and discover that rifts cluster far earlier than is generally observed with traditional means of capturing observations.
The only content related comment on this work is that the manuscript is missing a discussion on the potential discrepancies that arise due to a) the non-differentiation of crustal nature within the Somali plate (author models use a uniform continental plate rheology) and b) the absence of a key inheritance feature trending parallel to the extension direction, the Davie Fracture Zone.
The manuscript is well written and concise, and most other comments on this work are formative (consisting of missing scale bars in figures, acronyms, shortening sentences and possibly rephrasing some expressions).
Therefore, I recommend this work to be accepted for publication after these revisions are addressed.
For specific comments see below:
Dr Pavlos Farangitakis, Shell Global Solutions International
General comments:
I believe the manuscript would benefit from a discussion on how the difference in the nature of the crust (continental vs oceanic), would affect the evolution of the region. Between Madagascar and Mozambique, there is a stretch of a few 100s of kms of oceanic crust. I understand the limitations of analogue modelling and not being able to place different crustal compositions side by side in such an experiment, however it does merit a discussion point. I have added specific comments on where parts of this could fit through the manuscript

Further to the previous comment, part of the key pre-existing structural fabric is missing (such as the Davie Fracture Zone – see Phethean et al. 2016 or Reeves et al. 2016). Why do you consider this to not play a part on the EARS and do not include it in your set-up? It would be useful to see a discussion on what the omission of these two features (oceanic crust and Davie Fracture Zone) entails for your experiments (I suspect not much given that first order similarity is always the key outcome, however, will supplement the manuscript’s quality having captured the entirety of the key lithospheric features).

Specific comments:
(L10-15) Short summary: I am not sure whether this is also doubling as a plain language summary or not, if it is the case, consider adding in brackets in the first sentence that the “features splitting continents apart” are called rifts. If not, ignore this comment.
(L43-56) Introduction: What is missing from this section is a discussion/reference on the relative timing of each of the features on the EARS, particularly if references to inherited structures are made (such as the ones Glerum et al. 2020 refer to). Might be worth adding also some info on the map the further northward extension of the the Davie Fracture Zone, as you’d expect them to play a part in the plate configuration (See Phethean et al. 2016 this also refers to Fig 1 and later to the set-up).
Figure 1: Can you add the respective scale to each of the sub-panels?
(L84-93) Methods: I believe this section would benefit from a small 2-3 sentence section on highlighting the specific novelty of rotational analogue models in general (i.e. the works of Souriot and Brun 1992, Molnar et al. 2017, Farangitakis et al. 2019, 2021)
(L90-92) Methods: This sentence reads slightly odd. Consider breaking in two or putting the “at a rate of 4mm/h at the farthest point from the rotation axis” in a bracket.
(L95-101) Methods: Again, the DFZ is missing from the story here and the oceanic crust as well.
(L97-98) Methods: Consider also explaining how these seeds have also been used to simulate inheritance in rifted basins (such as the Gulf of Aden models in Autin et al. 2013).
(L143) Methods: I would like to see a bit more discussed on the 4 mm/h velocity since we are in a rotational environment and thus any velocity displays an “angular velocity” character. In line 90 it is mentioned this 4mm/h is the max velocity, so it is worth mentioning that going “south” in the rifted profile means velocities are less.
(L143) Methods: Why do you not consider this to be a major issue (answer might be my above comment)?
(L172) Methods: agisoft website needs its bracket to close
(L181-306) Results: There are references to Figures 3-7, such as to the “Malawi Rift”, that require the reader to revert back to Figures 1 and 2 to see where that is. Might be worth adding the names of the key features in panel (a) of each of the Figures 3-7.
(L331-372 or 415-475) Discussion: See “General comments 1 & 2”
(L423) Discussion: This is the first time that any feature’s relative timing is mentioned in the manuscript (see my earlier comment in the Introduction).
Figure 9: Please add scales to the image.
(L440) Discussion: I would refrain from using the phrase “all things considered” as it is quite informal.
(L449-465) Discussion: I recommend using one of the terms “microplate”, “micro plate” or “micro-plate” for consistency.

References:
Autin, J., Bellahsen, N., Leroy, S., Husson, L., Beslier, M. O., & d'Acremont, E. (2013). The role of structural inheritance in oblique rifting: Insights from analogue models and application to the Gulf of Aden. Tectonophysics, 607, 51-64.
Farangitakis, G. P., Sokoutis, D., McCaffrey, K. J., Willingshofer, E., Kalnins, L. M., Phethean, J. J., ... & van Steen, V. (2019). Analogue modeling of plate rotation effects in transform margins and rift‐transform intersections. Tectonics, 38(3), 823-841.
Farangitakis, G. P., McCaffrey, K. J., Willingshofer, E., Allen, M. B., Kalnins, L. M., van Hunen, J., ... & Sokoutis, D. (2021). The structural evolution of pull‐apart basins in response to changes in plate motion. Basin Research, 33(2), 1603-1625.
Glerum, A., Brune, S., Stamps, D. S., & Strecker, M. R. (2020). Victoria continental microplate dynamics controlled by the lithospheric strength distribution of the East African Rift. Nature Communications, 11(1), 2881.
Molnar, N. E., Cruden, A. R., & Betts, P. G. (2017). Interactions between propagating rotational rifts and linear rheological heterogeneities: Insights from three‐dimensional laboratory experiments. Tectonics, 36(3), 420-443.
Phethean, J. J., Kalnins, L. M., van Hunen, J., Biffi, P. G., Davies, R. J., & McCaffrey, K. J. (2016). Madagascar's escape from A frica: A high‐resolution plate reconstruction for the W estern S omali B asin and implications for supercontinent dispersal. Geochemistry, Geophysics, Geosystems, 17(12), 5036-5055.
Reeves, C. V., Teasdale, J. P., & Mahanjane, E. S. (2016). Insight into the Eastern Margin of Africa from a new tectonic model of the Indian Ocean. Geological Society, London, Special Publications, 431(1), 299-322.
Souriot, T., & Brun, J. P. (1992). Faulting and block rotation in the Afar triangle, East Africa: The Danakil" crank-arm" model. Geology, 20(10), 911-914.
Citation: https://doi.org/10.5194/egusphere-2022-1365-RC2
- AC1: 'Reply on RC2', Frank Zwaan, 29 Mar 2023
  
  We kindly thank the reviewer for the positive assessment of our manuscript, and have addressed the comments in the PDF file we uploaded.
  
  Citation: https://doi.org/10.5194/egusphere-2022-1365-AC1

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2022-1365', Cynthia Ebinger, 06 Feb 2023
Zwaan and Schreurs utilize fully scaled analogue models to investigate the role of rotational stresses on the continental-scale spatial evolution of rift zones, with comparison to rifting patterns in East Africa. The models explore a range of co-eval rift initiation geometries, and then track the time evolution of strain for comparison with the modern geometry of active rift zones in parts of E Africa. The models ignore rifting in the offshore SE rift branch in oceanic lithosphere east and southeast of the Rovuma block, and the SW branch that continues perhaps as far west as Angola around the San block.

My major concern with the paper is the reliance on outdated structural models based on coarse satellite imagery, and lacking information from seismicity and geodesy that shows modern plate motions. Specifically, the papers cited for the role of pre-existing basement shear zones are all based on satellite imagery and lack the 3^rd dimension – the dip of structures. Likewise, the age of some lineaments mapped in these publications remains speculative (e.g., Chorowicz, 2005), and papers utilizing displacement of data strata should only be considered.

The comparisons with data in Section 4.15 as well as model constraints need to be re-thought, and omission of processes (e.g., magmatism, GPE, etc) need to be clearly articulated.

Seismicity (Lindenfeld, M., Rümpker, G., Link, K., Koehn, D., & Batte, A. (2012). Fluid-triggered earthquake swarms in the Rwenzori region, East African Rift—Evidence for rift initiation. Tectonophysics, 566, 95-104; Lavayssière, A., Drooff, C., Ebinger, C., Gallacher, R., Illsley‐Kemp, F., Oliva, S. J., & Keir, D. (2019). Depth extent and kinematics of faulting in the southern Tanganyika rift, Africa. Tectonics, 38(3), 842-862; Ebinger, C. J., Oliva, S. J., Pham, T. Q., Peterson, K., Chindandali, P., Illsley‐Kemp, F., ... & Mulibo, G. (2019). Kinematics of active deformation in the Malawi rift and Rungwe Volcanic Province, Africa. Geochemistry, Geophysics, Geosystems, 20(8), 3928-3951; Weinstein, A., Oliva, S. J., Ebinger, C. J., Roecker, S., Tiberi, C., Aman, M., ... & Fischer, T. P. (2017). Fault‐magma interactions during early continental rifting: Seismicity of the M agadi‐N atron‐M anyara basins, A frica. Geochemistry, Geophysics, Geosystems, 18(10), 3662-3686; Zheng, W., Oliva, S. J., Ebinger, C., & Pritchard, M. E. (2020). Aseismic deformation during the 2014 M w 5.2 Karonga earthquake, Malawi, from satellite interferometry and earthquake source mechanisms. Geophysical Research Letters, 47(22), e2020GL090930) and geodetic strain from active plate motion and time-averaged strains (e.g., DeMets, C., & Merkouriev, S. (2021). Detailed reconstructions of India–Somalia Plate motion, 60 Ma to present: implications for Somalia Plate absolute motion and India–Eurasia Plate motion. Geophysical Journal International, 227(3), 1730-1767; Stamps, D. S., Kreemer, C., Fernandes, R., Rajaonarison, T. A., & Rambolamanana, G. (2021). Redefining east African rift system kinematics. Geology, 49(2), 150-155; Knappe, E., Bendick, R., Ebinger, C., Birhanu, Y., Lewi, E., Floyd, M., ... & Perry, M. (2020). Accommodation of East African rifting across the Turkana depression. Journal of Geophysical Research: Solid Earth, 125(2), e2019JB018469; Birhanu, Y., Bendick, R., Fisseha, S., Lewi, E., Floyd, M., King, R., & Reilinger, R. (2016). GPS constraints on broad scale extension in the Ethiopian Highlands and Main Ethiopian Rift. Geophysical Research Letters, 43(13), 6844-6851; Viltres, R., Jónsson, S., Ruch, J., Doubre, C., Reilinger, R., Floyd, M., & Ogubazghi, G. (2020). Kinematics and deformation of the southern Red Sea region from GPS observations. Geophysical Journal International, 221(3), 2143-2154.)

The authors cite decades-old papers to quote a N to S younging, inferring a N-S propagation of rifting throughout the EAR. Yet, the only two sectors of the EAR confirming that pattern are the Eastern rift in Kenya and N Tanzania, and the southern Malawi rift. The MER appears to have propagated from S to N, and the very poorly date Western rift may have initiated near the Rungwe volcanic province, and propagated both N and S from there (e.g., Roberts, E. M., Stevens, N. J., O’Connor, P. M., Dirks, P. H. G. M., Gottfried, M. D., Clyde, W. C., ... & Hemming, S. (2012). Initiation of the western branch of the East African Rift coeval with the eastern branch. Nature Geoscience, 5(4), 289-294.). See also Daly MC, Green P, Watts AB, Davies O, Chibesakunda F, and Walker R (2020) Tectonics and Landscape of the Central African Plateau, and their implications for a propagating
Southwestern Rift in Africa. Geochemistry, Geophysics, Geosystems. e2019GC008746. For information on the SW rift zone.

Other major concerns are as follows:

The EAR formed above one or more mantle plumes, and topographic relief within the region is > 1000 km. How do the authors include GPE? If not, tell the reader that it is ignored.

Likewise, parts of the study area have experienced 2+ km of magmatic underplate and have strain accommodated by magma intrusion. Since this is not included, tell the reader and consider the consequences.

Parts of the study area are underlain by cratonic roots that are 70 km thicker than surrounding areas. Since this is not considered, tell the reader and consider the consequences.

On what basis did the authors choose these models? Without careful consideration of the timing of diachronous rifting data, choice of models could be biased to outdated and inaccurate information.

Minor comments

Segments is generally used to describe a single fault-defined basin unit, whose length depends on the strength of the plate.

Line 48 - Strike slip faulting happens in accommodation zones and may reactivate a variety of basement sttructures, but overall, the rift structures form irrespective of basement structures. Please don't list my name there.

Line 53: What do you mean by an inherited weakness? THe 'weaknesses' are highly variable in the cited papers. What about the role of variable rheology linked to plate thickness (and hence geothermal gradient), composition, pre-existing thin zones, availability of melt, not just shear zones: see Muirhead et al., 2020;

Summary

The authors have published earlier papers considering rift models, which is in part why I urge them to dig more deeply into assumptions, and to move beyond EAR mythology to factual data constraining modern plate boundary deformation, and to move past lineament analyses.
Citation: https://doi.org/10.5194/egusphere-2022-1365-RC1
- AC2: 'Reply on RC1', Frank Zwaan, 29 Mar 2023
  
  We kindly thank the reviewer for the detailed assessment of our manuscript, and have addressed the comments in the PDF file we uploaded.
  
  Citation: https://doi.org/10.5194/egusphere-2022-1365-AC2
RC2:
'Comment on egusphere-2022-1365', Georgios-Pavlos Farangitakis, 11 Feb 2023
The authors present a novel analogue modelling approach through a rotating apparatus to delineate the evolution in response to rotational motions of rifts and use the East African Rift System as a natural example. They explore different rift-seed configurations and how these reflect on various features of the East African Rift System, making observations in the process about rotational stresses, microplate formation and preferential rift (re)activation.
A particularly novel part of this work is that the authors do a direct comparison on the initiation of a rift based on top-view photos, digital topography and particle tracing techniques and discover that rifts cluster far earlier than is generally observed with traditional means of capturing observations.
The only content related comment on this work is that the manuscript is missing a discussion on the potential discrepancies that arise due to a) the non-differentiation of crustal nature within the Somali plate (author models use a uniform continental plate rheology) and b) the absence of a key inheritance feature trending parallel to the extension direction, the Davie Fracture Zone.
The manuscript is well written and concise, and most other comments on this work are formative (consisting of missing scale bars in figures, acronyms, shortening sentences and possibly rephrasing some expressions).
Therefore, I recommend this work to be accepted for publication after these revisions are addressed.
For specific comments see below:
Dr Pavlos Farangitakis, Shell Global Solutions International
General comments:
I believe the manuscript would benefit from a discussion on how the difference in the nature of the crust (continental vs oceanic), would affect the evolution of the region. Between Madagascar and Mozambique, there is a stretch of a few 100s of kms of oceanic crust. I understand the limitations of analogue modelling and not being able to place different crustal compositions side by side in such an experiment, however it does merit a discussion point. I have added specific comments on where parts of this could fit through the manuscript

Further to the previous comment, part of the key pre-existing structural fabric is missing (such as the Davie Fracture Zone – see Phethean et al. 2016 or Reeves et al. 2016). Why do you consider this to not play a part on the EARS and do not include it in your set-up? It would be useful to see a discussion on what the omission of these two features (oceanic crust and Davie Fracture Zone) entails for your experiments (I suspect not much given that first order similarity is always the key outcome, however, will supplement the manuscript’s quality having captured the entirety of the key lithospheric features).

Specific comments:
(L10-15) Short summary: I am not sure whether this is also doubling as a plain language summary or not, if it is the case, consider adding in brackets in the first sentence that the “features splitting continents apart” are called rifts. If not, ignore this comment.
(L43-56) Introduction: What is missing from this section is a discussion/reference on the relative timing of each of the features on the EARS, particularly if references to inherited structures are made (such as the ones Glerum et al. 2020 refer to). Might be worth adding also some info on the map the further northward extension of the the Davie Fracture Zone, as you’d expect them to play a part in the plate configuration (See Phethean et al. 2016 this also refers to Fig 1 and later to the set-up).
Figure 1: Can you add the respective scale to each of the sub-panels?
(L84-93) Methods: I believe this section would benefit from a small 2-3 sentence section on highlighting the specific novelty of rotational analogue models in general (i.e. the works of Souriot and Brun 1992, Molnar et al. 2017, Farangitakis et al. 2019, 2021)
(L90-92) Methods: This sentence reads slightly odd. Consider breaking in two or putting the “at a rate of 4mm/h at the farthest point from the rotation axis” in a bracket.
(L95-101) Methods: Again, the DFZ is missing from the story here and the oceanic crust as well.
(L97-98) Methods: Consider also explaining how these seeds have also been used to simulate inheritance in rifted basins (such as the Gulf of Aden models in Autin et al. 2013).
(L143) Methods: I would like to see a bit more discussed on the 4 mm/h velocity since we are in a rotational environment and thus any velocity displays an “angular velocity” character. In line 90 it is mentioned this 4mm/h is the max velocity, so it is worth mentioning that going “south” in the rifted profile means velocities are less.
(L143) Methods: Why do you not consider this to be a major issue (answer might be my above comment)?
(L172) Methods: agisoft website needs its bracket to close
(L181-306) Results: There are references to Figures 3-7, such as to the “Malawi Rift”, that require the reader to revert back to Figures 1 and 2 to see where that is. Might be worth adding the names of the key features in panel (a) of each of the Figures 3-7.
(L331-372 or 415-475) Discussion: See “General comments 1 & 2”
(L423) Discussion: This is the first time that any feature’s relative timing is mentioned in the manuscript (see my earlier comment in the Introduction).
Figure 9: Please add scales to the image.
(L440) Discussion: I would refrain from using the phrase “all things considered” as it is quite informal.
(L449-465) Discussion: I recommend using one of the terms “microplate”, “micro plate” or “micro-plate” for consistency.

References:
Autin, J., Bellahsen, N., Leroy, S., Husson, L., Beslier, M. O., & d'Acremont, E. (2013). The role of structural inheritance in oblique rifting: Insights from analogue models and application to the Gulf of Aden. Tectonophysics, 607, 51-64.
Farangitakis, G. P., Sokoutis, D., McCaffrey, K. J., Willingshofer, E., Kalnins, L. M., Phethean, J. J., ... & van Steen, V. (2019). Analogue modeling of plate rotation effects in transform margins and rift‐transform intersections. Tectonics, 38(3), 823-841.
Farangitakis, G. P., McCaffrey, K. J., Willingshofer, E., Allen, M. B., Kalnins, L. M., van Hunen, J., ... & Sokoutis, D. (2021). The structural evolution of pull‐apart basins in response to changes in plate motion. Basin Research, 33(2), 1603-1625.
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Citation: https://doi.org/10.5194/egusphere-2022-1365-RC2
- AC1: 'Reply on RC2', Frank Zwaan, 29 Mar 2023
  
  We kindly thank the reviewer for the positive assessment of our manuscript, and have addressed the comments in the PDF file we uploaded.
  
  Citation: https://doi.org/10.5194/egusphere-2022-1365-AC1

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Frank Zwaan on behalf of the Authors (20 Apr 2023) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (27 May 2023) by Jordan J. J. Phethean

Dear Authors,

Many thanks for submitting your revised manuscript, which is improved thanks to the useful comments from reviewers. In particular, amendments made to the introduction, which update the literature basis for EARS inherited structures and extension velocity/propagation, and to the discussion, which make the work clearer/rigorous through detailing additional important limitations of the modelling approach, have improved the work.

In light of the revisions you have made following suggestions from the reviewers, I now recommend your manuscript for publication subject to technical corrections, which I outline below:

- In line 23 (Abstract), please clarify that ‘rotational rifting leads to the overall lateral propagation of deformation towards the rotation access”, to be consistent with your reply to Reviewer 1: “The Western Rift actually propagates in both directions (north and south) in our models, which is in fact in agreement with what the reviewer suggests.”. This sentence is also slightly long and complex, so I suggest to split it into two.

- Line 59, “comprising” is better changed to “comprises”.

- Line 76, “However” is not necessary here.

- Please take a moment review the written language within your introduction section (which has been subject to numerous revisions) to make sure sentences are now as clear for the reader as they can be. Please also replace some uses of “various” for more specific reference to publications or regions as relevant, which will be more informative for the reader.

- Please add a scale bar to figure 1a.

- Line 297, is the use of “deformation” as you intend in this sentence?

Many thanks,

Jordan

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ED: Publish subject to technical corrections (28 May 2023) by Federico Rossetti (Executive editor)

AR by Frank Zwaan on behalf of the Authors (03 Jun 2023) Author's response Manuscript

Journal article(s) based on this preprint

07 Aug 2023

The link between Somalian Plate rotation and the East African Rift System: an analogue modelling study

Frank Zwaan and Guido Schreurs

Solid Earth, 14, 823–845, https://doi.org/10.5194/se-14-823-2023,https://doi.org/10.5194/se-14-823-2023, 2023

Short summary

Frank Zwaan and Guido Schreurs

Data sets

Time-lapse imagery, digital image correlation (DIC) and topographic analysis of laboratory experiments simulating the evolution of the East African Rift System Frank Zwaan & Guido Schreurs https://www.dropbox.com/sh/6k34psul6cij4dh/AABpt-cnM1OyIEdolfTszmmya?dl=0

Frank Zwaan and Guido Schreurs

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

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The East African Rift System (EARS) is a major plate tectonic feature splitting the African continent apart. Understanding the tectonic processes involved is of great importance for societal and economic reasons (natural hazards, resources). Laboratory experiments allow us to simulate these large-scale processes, highlighting the impact of rotational plate motion on the overall development of the EARS, an insight relevant to our interpretation of other rift systems around the globe as well.


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