The development of rifting and magmatism in the multiply rifted Turkana Depression, East Africa: Evidence from surface-wave analysis of crustal and uppermost mantle structure

R. Kounoudis; I. D. Bastow; C. J. Ebinger; F. Darbyshire; C. S. Ogden; M. Musila; F. Ugo; A. Ayele; G. Sullivan; R. Bendick; N. Mariita; G. Kianji

doi:10.1016/j.epsl.2023.118386

The development of rifting and magmatism in the multiply rifted Turkana Depression, East Africa: Evidence from surface-wave analysis of crustal and uppermost mantle structure

R. Kounoudis, I. D. Bastow, C. J. Ebinger, F. Darbyshire, C. S. Ogden, M. Musila, F. Ugo, A. Ayele, G. Sullivan, R. Bendick, N. Mariita, G. Kianji

Geosciences

Research output: Contribution to journal › Article › peer-review

10 Scopus citations

Abstract

The Turkana Depression separates the uplifted Ethiopian and East African Plateaus. It was the site, in Mesozoic times, of a failed episode of NE–SW-oriented rifting (the Anza Rift), but now hosts E–W-oriented Nubia–Somalia separation at the junction between the Main Ethiopian Rift in the north and the Eastern Rift to the south. However, the time-integrated effect of these rifting phases on crustal and lithospheric mantle architecture and thermal structure is poorly understood. Utilising data from new seismograph networks in the Turkana Depression and northern Tanzania Craton, we produce a detailed anisotropic crustal and uppermost mantle shear-wave velocity model of the region. Within the Tanzania Craton, slightly lower uppermost mantle wavespeeds (4.4–4.5 km/s) compared to neighbouring regions, and coincident rift-parallel crustal anisotropy, imply the Nyanza Rift developed in relatively weak mobile belt lithosphere between two refractory Archean blocks. At upper-crustal (≲10 km) depths in the Turkana Depression, the slowest velocities (≲3.2 km/s) are attributed to thick Mesozoic-age sedimentary basins. Nowhere within the Depression is the mid-to-lower crust or lithospheric mantle associated with wavespeeds as slow, or seismic anisotropy as strong, as that observed below the melt-rich central and northern Main Ethiopian Rift (MER) and Ethiopian Plateau further north. High upper mantle wavespeeds (≳4.5 km/s), coinciding with the broadening of MER-rifting into southern Ethiopia, confirm the presence of refractory Proterozoic lithosphere acting as a rheological boundary to rift development. Thinned crustal zones associated with failed Mesozoic Anza rifting are also underlain by fast wavespeed (>4.5 km/s) mantle lithosphere, implying this area has resisted significant thermomechanical modification from Miocene-Recent extension and magmatism. Pre-existing crustal thin zones do not, therefore, necessarily represent zones of plate-weakness where subsequent phases of rifting will develop.

Original language	English
Article number	118386
Journal	Earth and Planetary Science Letters
Volume	621
DOIs	https://doi.org/10.1016/j.epsl.2023.118386
State	Published - Nov 1 2023

Funding

We thank Chris Morley and an anonymous reviewer for insightful reviews. Data for TRAILS seismograph networks Y1 ( Ebinger, 2018 ) and 6R ( Bastow, 2019 ) were sourced via the Incorporated Research Institutions for Seismology (IRIS) Data Management Centre ( https://ds.iris.edu/ds/nodes/dmc ). The SEIS-UK data management facility provided seismograph instruments deployed in southern Ethiopia ( Bastow, 2019 ). The seismograph instruments deployed in Kenya ( Ebinger, 2018 ) were provided by IRIS through the PASSCAL Instrument Centre at New Mexico Tech. The facilities of IRIS Data Services, and specifically the IRIS Data Management Centre, were used for access to waveforms, related metadata, and/or derived products used in this study for the ZP ( Nyblade, 2007 ), XW ( Nyblade, 2017 ), 1C ( Velasco et al., 2011 ), YY ( Keranen, 2013 ), and XI ( Nyblade, 2000 ) networks. Seismic data for network GE were obtained from the GEOFON data centre of the GFZ German Research Centre for Geosciences. We acknowledge collaboration with the University of Nairobi and Addis Ababa University, including their help establishing the TRAILS network. J. Mechie kindly provided access to data from the KRISP project. We thank T. Rooney for insightful discussions. R. Kounoudis is funded by an Imperial College President's PhD Scholarship. C. Ebinger acknowledges NSFGEO-NERC award 1824417 . This work was supported by the Natural Environment Research Council , grant numbers NE/S014136/1 and NE/L002515/1 . For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript (AAM) version arising. We thank Chris Morley and an anonymous reviewer for insightful reviews. Data for TRAILS seismograph networks Y1 (Ebinger, 2018) and 6R (Bastow, 2019) were sourced via the Incorporated Research Institutions for Seismology (IRIS) Data Management Centre (https://ds.iris.edu/ds/nodes/dmc). The SEIS-UK data management facility provided seismograph instruments deployed in southern Ethiopia (Bastow, 2019). The seismograph instruments deployed in Kenya (Ebinger, 2018) were provided by IRIS through the PASSCAL Instrument Centre at New Mexico Tech. The facilities of IRIS Data Services, and specifically the IRIS Data Management Centre, were used for access to waveforms, related metadata, and/or derived products used in this study for the ZP (Nyblade, 2007), XW (Nyblade, 2017), 1C (Velasco et al. 2011), YY (Keranen, 2013), and XI (Nyblade, 2000) networks. Seismic data for network GE were obtained from the GEOFON data centre of the GFZ German Research Centre for Geosciences. We acknowledge collaboration with the University of Nairobi and Addis Ababa University, including their help establishing the TRAILS network. J. Mechie kindly provided access to data from the KRISP project. We thank T. Rooney for insightful discussions. R. Kounoudis is funded by an Imperial College President's PhD Scholarship. C. Ebinger acknowledges NSFGEO-NERC award 1824417. This work was supported by the Natural Environment Research Council, grant numbers NE/S014136/1 and NE/L002515/1. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript (AAM) version arising.

Funders	Funder number
1824417
Natural Environment Research Council	NE/L002515/1, NE/S014136/1

Keywords

East African Rift
Turkana Depression
azimuthal anisotropy
continental rifting
crustal and uppermost mantle structure
surface-wave tomography

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10.1016/j.epsl.2023.118386

Cite this

Kounoudis, R., Bastow, I. D., Ebinger, C. J., Darbyshire, F., Ogden, C. S., Musila, M., Ugo, F., Ayele, A., Sullivan, G., Bendick, R., Mariita, N., & Kianji, G. (2023). The development of rifting and magmatism in the multiply rifted Turkana Depression, East Africa: Evidence from surface-wave analysis of crustal and uppermost mantle structure. Earth and Planetary Science Letters, 621, Article 118386. https://doi.org/10.1016/j.epsl.2023.118386

@article{ecd6a0d67adc4ace92583ec6e1eb3150,

title = "The development of rifting and magmatism in the multiply rifted Turkana Depression, East Africa: Evidence from surface-wave analysis of crustal and uppermost mantle structure",

abstract = "The Turkana Depression separates the uplifted Ethiopian and East African Plateaus. It was the site, in Mesozoic times, of a failed episode of NE–SW-oriented rifting (the Anza Rift), but now hosts E–W-oriented Nubia–Somalia separation at the junction between the Main Ethiopian Rift in the north and the Eastern Rift to the south. However, the time-integrated effect of these rifting phases on crustal and lithospheric mantle architecture and thermal structure is poorly understood. Utilising data from new seismograph networks in the Turkana Depression and northern Tanzania Craton, we produce a detailed anisotropic crustal and uppermost mantle shear-wave velocity model of the region. Within the Tanzania Craton, slightly lower uppermost mantle wavespeeds (4.4–4.5 km/s) compared to neighbouring regions, and coincident rift-parallel crustal anisotropy, imply the Nyanza Rift developed in relatively weak mobile belt lithosphere between two refractory Archean blocks. At upper-crustal (≲10 km) depths in the Turkana Depression, the slowest velocities (≲3.2 km/s) are attributed to thick Mesozoic-age sedimentary basins. Nowhere within the Depression is the mid-to-lower crust or lithospheric mantle associated with wavespeeds as slow, or seismic anisotropy as strong, as that observed below the melt-rich central and northern Main Ethiopian Rift (MER) and Ethiopian Plateau further north. High upper mantle wavespeeds (≳4.5 km/s), coinciding with the broadening of MER-rifting into southern Ethiopia, confirm the presence of refractory Proterozoic lithosphere acting as a rheological boundary to rift development. Thinned crustal zones associated with failed Mesozoic Anza rifting are also underlain by fast wavespeed (>4.5 km/s) mantle lithosphere, implying this area has resisted significant thermomechanical modification from Miocene-Recent extension and magmatism. Pre-existing crustal thin zones do not, therefore, necessarily represent zones of plate-weakness where subsequent phases of rifting will develop.",

keywords = "East African Rift, Turkana Depression, azimuthal anisotropy, continental rifting, crustal and uppermost mantle structure, surface-wave tomography",

author = "R. Kounoudis and Bastow, \{I. D.\} and Ebinger, \{C. J.\} and F. Darbyshire and Ogden, \{C. S.\} and M. Musila and F. Ugo and A. Ayele and G. Sullivan and R. Bendick and N. Mariita and G. Kianji",

note = "Funding Information: We thank Chris Morley and an anonymous reviewer for insightful reviews. Data for TRAILS seismograph networks Y1 ( Ebinger, 2018 ) and 6R ( Bastow, 2019 ) were sourced via the Incorporated Research Institutions for Seismology (IRIS) Data Management Centre ( https://ds.iris.edu/ds/nodes/dmc ). The SEIS-UK data management facility provided seismograph instruments deployed in southern Ethiopia ( Bastow, 2019 ). The seismograph instruments deployed in Kenya ( Ebinger, 2018 ) were provided by IRIS through the PASSCAL Instrument Centre at New Mexico Tech. The facilities of IRIS Data Services, and specifically the IRIS Data Management Centre, were used for access to waveforms, related metadata, and/or derived products used in this study for the ZP ( Nyblade, 2007 ), XW ( Nyblade, 2017 ), 1C ( Velasco et al., 2011 ), YY ( Keranen, 2013 ), and XI ( Nyblade, 2000 ) networks. Seismic data for network GE were obtained from the GEOFON data centre of the GFZ German Research Centre for Geosciences. We acknowledge collaboration with the University of Nairobi and Addis Ababa University, including their help establishing the TRAILS network. J. Mechie kindly provided access to data from the KRISP project. We thank T. Rooney for insightful discussions. R. Kounoudis is funded by an Imperial College President's PhD Scholarship. C. Ebinger acknowledges NSFGEO-NERC award 1824417 . This work was supported by the Natural Environment Research Council , grant numbers NE/S014136/1 and NE/L002515/1 . For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript (AAM) version arising. Funding Information: We thank Chris Morley and an anonymous reviewer for insightful reviews. Data for TRAILS seismograph networks Y1 (Ebinger, 2018) and 6R (Bastow, 2019) were sourced via the Incorporated Research Institutions for Seismology (IRIS) Data Management Centre (https://ds.iris.edu/ds/nodes/dmc). The SEIS-UK data management facility provided seismograph instruments deployed in southern Ethiopia (Bastow, 2019). The seismograph instruments deployed in Kenya (Ebinger, 2018) were provided by IRIS through the PASSCAL Instrument Centre at New Mexico Tech. The facilities of IRIS Data Services, and specifically the IRIS Data Management Centre, were used for access to waveforms, related metadata, and/or derived products used in this study for the ZP (Nyblade, 2007), XW (Nyblade, 2017), 1C (Velasco et al. 2011), YY (Keranen, 2013), and XI (Nyblade, 2000) networks. Seismic data for network GE were obtained from the GEOFON data centre of the GFZ German Research Centre for Geosciences. We acknowledge collaboration with the University of Nairobi and Addis Ababa University, including their help establishing the TRAILS network. J. Mechie kindly provided access to data from the KRISP project. We thank T. Rooney for insightful discussions. R. Kounoudis is funded by an Imperial College President's PhD Scholarship. C. Ebinger acknowledges NSFGEO-NERC award 1824417. This work was supported by the Natural Environment Research Council, grant numbers NE/S014136/1 and NE/L002515/1. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript (AAM) version arising. Publisher Copyright: {\textcopyright} 2023 The Author(s)",

year = "2023",

month = nov,

day = "1",

doi = "10.1016/j.epsl.2023.118386",

language = "English",

volume = "621",

journal = "Earth and Planetary Science Letters",

issn = "0012-821X",

publisher = "Elsevier B.V.",

}

Kounoudis, R, Bastow, ID, Ebinger, CJ, Darbyshire, F, Ogden, CS, Musila, M, Ugo, F, Ayele, A, Sullivan, G, Bendick, R, Mariita, N & Kianji, G 2023, 'The development of rifting and magmatism in the multiply rifted Turkana Depression, East Africa: Evidence from surface-wave analysis of crustal and uppermost mantle structure', Earth and Planetary Science Letters, vol. 621, 118386. https://doi.org/10.1016/j.epsl.2023.118386

TY - JOUR

T1 - The development of rifting and magmatism in the multiply rifted Turkana Depression, East Africa

T2 - Evidence from surface-wave analysis of crustal and uppermost mantle structure

AU - Kounoudis, R.

AU - Bastow, I. D.

AU - Ebinger, C. J.

AU - Darbyshire, F.

AU - Ogden, C. S.

AU - Musila, M.

AU - Ugo, F.

AU - Ayele, A.

AU - Sullivan, G.

AU - Bendick, R.

AU - Mariita, N.

AU - Kianji, G.

N1 - Funding Information: We thank Chris Morley and an anonymous reviewer for insightful reviews. Data for TRAILS seismograph networks Y1 ( Ebinger, 2018 ) and 6R ( Bastow, 2019 ) were sourced via the Incorporated Research Institutions for Seismology (IRIS) Data Management Centre ( https://ds.iris.edu/ds/nodes/dmc ). The SEIS-UK data management facility provided seismograph instruments deployed in southern Ethiopia ( Bastow, 2019 ). The seismograph instruments deployed in Kenya ( Ebinger, 2018 ) were provided by IRIS through the PASSCAL Instrument Centre at New Mexico Tech. The facilities of IRIS Data Services, and specifically the IRIS Data Management Centre, were used for access to waveforms, related metadata, and/or derived products used in this study for the ZP ( Nyblade, 2007 ), XW ( Nyblade, 2017 ), 1C ( Velasco et al., 2011 ), YY ( Keranen, 2013 ), and XI ( Nyblade, 2000 ) networks. Seismic data for network GE were obtained from the GEOFON data centre of the GFZ German Research Centre for Geosciences. We acknowledge collaboration with the University of Nairobi and Addis Ababa University, including their help establishing the TRAILS network. J. Mechie kindly provided access to data from the KRISP project. We thank T. Rooney for insightful discussions. R. Kounoudis is funded by an Imperial College President's PhD Scholarship. C. Ebinger acknowledges NSFGEO-NERC award 1824417 . This work was supported by the Natural Environment Research Council , grant numbers NE/S014136/1 and NE/L002515/1 . For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript (AAM) version arising. Funding Information: We thank Chris Morley and an anonymous reviewer for insightful reviews. Data for TRAILS seismograph networks Y1 (Ebinger, 2018) and 6R (Bastow, 2019) were sourced via the Incorporated Research Institutions for Seismology (IRIS) Data Management Centre (https://ds.iris.edu/ds/nodes/dmc). The SEIS-UK data management facility provided seismograph instruments deployed in southern Ethiopia (Bastow, 2019). The seismograph instruments deployed in Kenya (Ebinger, 2018) were provided by IRIS through the PASSCAL Instrument Centre at New Mexico Tech. The facilities of IRIS Data Services, and specifically the IRIS Data Management Centre, were used for access to waveforms, related metadata, and/or derived products used in this study for the ZP (Nyblade, 2007), XW (Nyblade, 2017), 1C (Velasco et al. 2011), YY (Keranen, 2013), and XI (Nyblade, 2000) networks. Seismic data for network GE were obtained from the GEOFON data centre of the GFZ German Research Centre for Geosciences. We acknowledge collaboration with the University of Nairobi and Addis Ababa University, including their help establishing the TRAILS network. J. Mechie kindly provided access to data from the KRISP project. We thank T. Rooney for insightful discussions. R. Kounoudis is funded by an Imperial College President's PhD Scholarship. C. Ebinger acknowledges NSFGEO-NERC award 1824417. This work was supported by the Natural Environment Research Council, grant numbers NE/S014136/1 and NE/L002515/1. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript (AAM) version arising. Publisher Copyright: © 2023 The Author(s)

PY - 2023/11/1

Y1 - 2023/11/1

N2 - The Turkana Depression separates the uplifted Ethiopian and East African Plateaus. It was the site, in Mesozoic times, of a failed episode of NE–SW-oriented rifting (the Anza Rift), but now hosts E–W-oriented Nubia–Somalia separation at the junction between the Main Ethiopian Rift in the north and the Eastern Rift to the south. However, the time-integrated effect of these rifting phases on crustal and lithospheric mantle architecture and thermal structure is poorly understood. Utilising data from new seismograph networks in the Turkana Depression and northern Tanzania Craton, we produce a detailed anisotropic crustal and uppermost mantle shear-wave velocity model of the region. Within the Tanzania Craton, slightly lower uppermost mantle wavespeeds (4.4–4.5 km/s) compared to neighbouring regions, and coincident rift-parallel crustal anisotropy, imply the Nyanza Rift developed in relatively weak mobile belt lithosphere between two refractory Archean blocks. At upper-crustal (≲10 km) depths in the Turkana Depression, the slowest velocities (≲3.2 km/s) are attributed to thick Mesozoic-age sedimentary basins. Nowhere within the Depression is the mid-to-lower crust or lithospheric mantle associated with wavespeeds as slow, or seismic anisotropy as strong, as that observed below the melt-rich central and northern Main Ethiopian Rift (MER) and Ethiopian Plateau further north. High upper mantle wavespeeds (≳4.5 km/s), coinciding with the broadening of MER-rifting into southern Ethiopia, confirm the presence of refractory Proterozoic lithosphere acting as a rheological boundary to rift development. Thinned crustal zones associated with failed Mesozoic Anza rifting are also underlain by fast wavespeed (>4.5 km/s) mantle lithosphere, implying this area has resisted significant thermomechanical modification from Miocene-Recent extension and magmatism. Pre-existing crustal thin zones do not, therefore, necessarily represent zones of plate-weakness where subsequent phases of rifting will develop.

AB - The Turkana Depression separates the uplifted Ethiopian and East African Plateaus. It was the site, in Mesozoic times, of a failed episode of NE–SW-oriented rifting (the Anza Rift), but now hosts E–W-oriented Nubia–Somalia separation at the junction between the Main Ethiopian Rift in the north and the Eastern Rift to the south. However, the time-integrated effect of these rifting phases on crustal and lithospheric mantle architecture and thermal structure is poorly understood. Utilising data from new seismograph networks in the Turkana Depression and northern Tanzania Craton, we produce a detailed anisotropic crustal and uppermost mantle shear-wave velocity model of the region. Within the Tanzania Craton, slightly lower uppermost mantle wavespeeds (4.4–4.5 km/s) compared to neighbouring regions, and coincident rift-parallel crustal anisotropy, imply the Nyanza Rift developed in relatively weak mobile belt lithosphere between two refractory Archean blocks. At upper-crustal (≲10 km) depths in the Turkana Depression, the slowest velocities (≲3.2 km/s) are attributed to thick Mesozoic-age sedimentary basins. Nowhere within the Depression is the mid-to-lower crust or lithospheric mantle associated with wavespeeds as slow, or seismic anisotropy as strong, as that observed below the melt-rich central and northern Main Ethiopian Rift (MER) and Ethiopian Plateau further north. High upper mantle wavespeeds (≳4.5 km/s), coinciding with the broadening of MER-rifting into southern Ethiopia, confirm the presence of refractory Proterozoic lithosphere acting as a rheological boundary to rift development. Thinned crustal zones associated with failed Mesozoic Anza rifting are also underlain by fast wavespeed (>4.5 km/s) mantle lithosphere, implying this area has resisted significant thermomechanical modification from Miocene-Recent extension and magmatism. Pre-existing crustal thin zones do not, therefore, necessarily represent zones of plate-weakness where subsequent phases of rifting will develop.

KW - East African Rift

KW - Turkana Depression

KW - azimuthal anisotropy

KW - continental rifting

KW - crustal and uppermost mantle structure

KW - surface-wave tomography

UR - https://www.scopus.com/pages/publications/85172186322

U2 - 10.1016/j.epsl.2023.118386

DO - 10.1016/j.epsl.2023.118386

M3 - Article

AN - SCOPUS:85172186322

SN - 0012-821X

VL - 621

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

M1 - 118386

ER -

The development of rifting and magmatism in the multiply rifted Turkana Depression, East Africa: Evidence from surface-wave analysis of crustal and uppermost mantle structure

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