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Crustal structure at a young continental rift: a receiver function study from the Tanganyika Rift

Crustal structure at a young continental rift: a receiver function study from the Tanganyika Rift
Crustal structure at a young continental rift: a receiver function study from the Tanganyika Rift
The southern Tanganyika Rift, within the Western rift, Africa, has earthquakes to depths of 37 km, yet few constraints exist on crustal thickness, or of early stage rifting processes in apparently amagmatic rift sectors. The aim of the TANGA14 experiment was to constrain bulk crustal properties to test whether magmatic processes modify the lithosphere in areas of deep seismicity, and the degree of lithospheric thinning. We use eleven broadband seismometers to implement receiver function analysis using H-κ stacking, a method sensitive to crustal thickness and VP/VS ratio, to determine bulk crustal properties. Analyses include extensive error analysis through bootstrap, variance and phase-weighted stacking. Results show the Archean Tanzanian Craton and Bangweulu Block are characterized by VP/VS ratios of 1.75-1.77, implying a felsic bulk composition. Crust beneath the fault bounded basins has high VP/VS (>1.9). Anorthosite bodies and surface sediments within the region may contribute to localized high VP/VS. However, elevated VP/VS values within fault-bounded extensional basins where elevated heat flow, hydrothermal vent sites, and deep earthquakes are observed suggest that magma may be intruding the lower crust beneath the southern Tanganyika Rift. Crustal thicknesses on/near the relatively un-extended Tanzanian craton and Bangweulu Block are 41.6-42.0 km. This contrasts with the Tanganyika Rift where crustal thicknesses are 31.6 km to 39 km from north to south. Our results provide evidence for ~20% crustal thinning localized to fault-bounded basins. Taken together, they suggest a previously unrecognized role of magma intrusion in early-stage continental rifting in the Western rift, Africa.
0278-7407
1-31
Hodgson, Isabel
3f51251e-9bf1-4360-b99c-19fbbfffc32b
Illsley-Kemp, Finnigan
c24ef4cb-cbf9-4a58-af8d-da9c7eabd84d
Gallacher, Ryan J.
689f755f-b4a0-4a3b-9959-93c2fae0ac2c
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Ebinger, Cynthia J.
9aab3b18-294f-4cda-b64d-375b1cae85bb
Mtelela, Khalfan
bf5619a0-6020-4469-b0fd-48a7629e2bfb
Hodgson, Isabel
3f51251e-9bf1-4360-b99c-19fbbfffc32b
Illsley-Kemp, Finnigan
c24ef4cb-cbf9-4a58-af8d-da9c7eabd84d
Gallacher, Ryan J.
689f755f-b4a0-4a3b-9959-93c2fae0ac2c
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Ebinger, Cynthia J.
9aab3b18-294f-4cda-b64d-375b1cae85bb
Mtelela, Khalfan
bf5619a0-6020-4469-b0fd-48a7629e2bfb

Hodgson, Isabel, Illsley-Kemp, Finnigan, Gallacher, Ryan J., Keir, Derek, Ebinger, Cynthia J. and Mtelela, Khalfan (2017) Crustal structure at a young continental rift: a receiver function study from the Tanganyika Rift. Tectonics, 1-31. (doi:10.1002/2017TC004477).

Record type: Article

Abstract

The southern Tanganyika Rift, within the Western rift, Africa, has earthquakes to depths of 37 km, yet few constraints exist on crustal thickness, or of early stage rifting processes in apparently amagmatic rift sectors. The aim of the TANGA14 experiment was to constrain bulk crustal properties to test whether magmatic processes modify the lithosphere in areas of deep seismicity, and the degree of lithospheric thinning. We use eleven broadband seismometers to implement receiver function analysis using H-κ stacking, a method sensitive to crustal thickness and VP/VS ratio, to determine bulk crustal properties. Analyses include extensive error analysis through bootstrap, variance and phase-weighted stacking. Results show the Archean Tanzanian Craton and Bangweulu Block are characterized by VP/VS ratios of 1.75-1.77, implying a felsic bulk composition. Crust beneath the fault bounded basins has high VP/VS (>1.9). Anorthosite bodies and surface sediments within the region may contribute to localized high VP/VS. However, elevated VP/VS values within fault-bounded extensional basins where elevated heat flow, hydrothermal vent sites, and deep earthquakes are observed suggest that magma may be intruding the lower crust beneath the southern Tanganyika Rift. Crustal thicknesses on/near the relatively un-extended Tanzanian craton and Bangweulu Block are 41.6-42.0 km. This contrasts with the Tanganyika Rift where crustal thicknesses are 31.6 km to 39 km from north to south. Our results provide evidence for ~20% crustal thinning localized to fault-bounded basins. Taken together, they suggest a previously unrecognized role of magma intrusion in early-stage continental rifting in the Western rift, Africa.

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Accepted/In Press date: 18 October 2017
e-pub ahead of print date: 13 November 2017

Identifiers

Local EPrints ID: 415520
URI: http://eprints.soton.ac.uk/id/eprint/415520
ISSN: 0278-7407
PURE UUID: 39b4d4bd-7391-4d33-9d5f-adfc8ed26f3e
ORCID for Finnigan Illsley-Kemp: ORCID iD orcid.org/0000-0002-7114-033X
ORCID for Derek Keir: ORCID iD orcid.org/0000-0001-8787-8446

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Date deposited: 14 Nov 2017 17:30
Last modified: 28 Jan 2022 05:02

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Contributors

Author: Isabel Hodgson
Author: Finnigan Illsley-Kemp ORCID iD
Author: Ryan J. Gallacher
Author: Derek Keir ORCID iD
Author: Cynthia J. Ebinger
Author: Khalfan Mtelela

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