Magmatic evolution during proto-oceanic rifting at Alu, Dalafilla and Borale Volcanoes (Afar) determined by trace element and Sr-Nd-Pb isotope geochemistry
Magmatic evolution during proto-oceanic rifting at Alu, Dalafilla and Borale Volcanoes (Afar) determined by trace element and Sr-Nd-Pb isotope geochemistry
Continental rifting and associated magmatism can eventually result in the formation of new ocean basins. However, the characteristics of magmatism in the latest stages of rifting are poorly understood. The Erta-Ale volcanic segment (EAVS) in the Danakil Depression of Afar, Ethiopia, provides a unique natural laboratory in which to investigate how magma generation evolves during the shift from continental rifting to oceanic spreading. Here we present new trace element data combined with Sr-Nd-Pb isotope ratios for three volcanoes, Alu, Dalafilla and Borale, in the north of the EAVS. These data shed light on the changes in melt production and storage that occur at this late stage in the rifting cycle. Elevated Ce/Pb and ΔNb (33–48, 0.25–0.47 respectively) of the basalts, alongside Sr-Nd-Pb isotope geochemistry indicate the presence of a HIMU component, supplied by the Afar plume, together with contamination by the crust. Melting conditions, estimated using the trace element ratios, Smn/Ybn, Dyn/Ybn and Cen/Smn, indicate that magmas were primarily derived from spinel lherzolite (85–90%) with minor garnet lherzolite (10–15%) with a melt fraction of ~4%. Melt-mantle equilibrium depths are estimated to be on the order of 64 to 83 km, shallower than that previously inferred within Afar. We suggest that this is likely a result of the more plate thinning beneath the EAVS compared to other parts of Afar. Basaltic volcanics are found to have heterogeneous Sr-Nd-Pb isotope compositions whilst those more evolved rocks (i.e., SiO2 ≥52 wt%) exhibit consistent radiogenic compositions. This indicates that homogenisation of all melt compositions occurs prior-to or during melt differentiation, with the latter process occurring rapidly in upper crust with minimal crustal contamination. Overall whilst the Afar plume appears to be the dominant mantle component in the volcanic rocks, the melt characteristics and magmatic storage conditions beneath the EAVS shows variability that is likely controlled by a dynamic interplay between rifting and mantle processes.
Continental-rifting, Radiogenic-isotope, Trace-elements, Volcanic-plumbing-system
Watts, Emma J.
2135079d-2472-4d7e-a05a-3f234793697e
Gernon, Thomas
658041a0-fdd1-4516-85f4-98895a39235e
Taylor, Rex N
094be7fd-ef61-4acd-a795-7daba2bc6183
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Pagli, Carolina
290edb22-712b-4563-a868-af4c21fdb6b0
21 August 2023
Watts, Emma J.
2135079d-2472-4d7e-a05a-3f234793697e
Gernon, Thomas
658041a0-fdd1-4516-85f4-98895a39235e
Taylor, Rex N
094be7fd-ef61-4acd-a795-7daba2bc6183
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Pagli, Carolina
290edb22-712b-4563-a868-af4c21fdb6b0
Watts, Emma J., Gernon, Thomas, Taylor, Rex N, Keir, Derek and Pagli, Carolina
(2023)
Magmatic evolution during proto-oceanic rifting at Alu, Dalafilla and Borale Volcanoes (Afar) determined by trace element and Sr-Nd-Pb isotope geochemistry.
Lithos, 456-457, [107311].
(doi:10.1016/j.lithos.2023.107311).
Abstract
Continental rifting and associated magmatism can eventually result in the formation of new ocean basins. However, the characteristics of magmatism in the latest stages of rifting are poorly understood. The Erta-Ale volcanic segment (EAVS) in the Danakil Depression of Afar, Ethiopia, provides a unique natural laboratory in which to investigate how magma generation evolves during the shift from continental rifting to oceanic spreading. Here we present new trace element data combined with Sr-Nd-Pb isotope ratios for three volcanoes, Alu, Dalafilla and Borale, in the north of the EAVS. These data shed light on the changes in melt production and storage that occur at this late stage in the rifting cycle. Elevated Ce/Pb and ΔNb (33–48, 0.25–0.47 respectively) of the basalts, alongside Sr-Nd-Pb isotope geochemistry indicate the presence of a HIMU component, supplied by the Afar plume, together with contamination by the crust. Melting conditions, estimated using the trace element ratios, Smn/Ybn, Dyn/Ybn and Cen/Smn, indicate that magmas were primarily derived from spinel lherzolite (85–90%) with minor garnet lherzolite (10–15%) with a melt fraction of ~4%. Melt-mantle equilibrium depths are estimated to be on the order of 64 to 83 km, shallower than that previously inferred within Afar. We suggest that this is likely a result of the more plate thinning beneath the EAVS compared to other parts of Afar. Basaltic volcanics are found to have heterogeneous Sr-Nd-Pb isotope compositions whilst those more evolved rocks (i.e., SiO2 ≥52 wt%) exhibit consistent radiogenic compositions. This indicates that homogenisation of all melt compositions occurs prior-to or during melt differentiation, with the latter process occurring rapidly in upper crust with minimal crustal contamination. Overall whilst the Afar plume appears to be the dominant mantle component in the volcanic rocks, the melt characteristics and magmatic storage conditions beneath the EAVS shows variability that is likely controlled by a dynamic interplay between rifting and mantle processes.
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Accepted/In Press date: 3 August 2023
e-pub ahead of print date: 7 August 2023
Published date: 21 August 2023
Additional Information:
Funding Information:
This research was funded by the Natural Environmental Research Council [grant number NE/L002531/1 ]. E.J.W was supported by the Wyley Fund of the Geologists' Association. T.M.G was supported by a Natural Environmental Research Council grant [NE/R004978/1]. D.K. and C.P., are funded by 2017 PRIN project - protocol MIUR: 2017P9AT72 PE10. We acknowledge the use of rocks from the Afar Repository of the University of Pisa, Italy ( http://repositories.dst.unipi.it/index.php/home-afar ). We acknowledge all those involved in the field-campaign in the 1960s. We thank Laura De Dosso for her help with the Afar Repository samples. We thank Matthew Cooper, Agnes Michalik and Andy Milton for their help and expert guidance with the laboratory work. We thank Gianmaria Tortelli for his discussions about volcanism within the region. We also thank the editor Dr. Greg Shellnutt as well as Dr. Karine Carvas and an anonymous reviewer for their constructive comments on the manuscript.
Funding Information:
This research was funded by the Natural Environmental Research Council [grant number NE/L002531/1]. E.J.W was supported by the Wyley Fund of the Geologists' Association. T.M.G was supported by a Natural Environmental Research Council grant [NE/R004978/1]. D.K. and C.P. are funded by 2017 PRIN project - protocol MIUR: 2017P9AT72 PE10. We acknowledge the use of rocks from the Afar Repository of the University of Pisa, Italy (http://repositories.dst.unipi.it/index.php/home-afar). We acknowledge all those involved in the field-campaign in the 1960s. We thank Laura De Dosso for her help with the Afar Repository samples. We thank Matthew Cooper, Agnes Michalik and Andy Milton for their help and expert guidance with the laboratory work. We thank Gianmaria Tortelli for his discussions about volcanism within the region. We also thank the editor Dr. Greg Shellnutt as well as Dr. Karine Carvas and an anonymous reviewer for their constructive comments on the manuscript.
Keywords:
Continental-rifting, Radiogenic-isotope, Trace-elements, Volcanic-plumbing-system
Identifiers
Local EPrints ID: 481209
URI: http://eprints.soton.ac.uk/id/eprint/481209
ISSN: 0024-4937
PURE UUID: 4ac9e949-69ec-4e58-ba25-4cafd3971a91
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Date deposited: 18 Aug 2023 16:43
Last modified: 27 Apr 2024 02:22
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Author:
Emma J. Watts
Author:
Carolina Pagli
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