Body‐Wave Tomographic Imaging of the Turkana Depression: Implications for Rift Development and Plume‐Lithosphere Interactions

Kounoudis, R.; Bastow, I. D.; Ebinger, C. J.; Ogden, C. S.; Ayele, Atalay; Bendick, Rebecca; Mariita, Nicholas; Kianji, G.; Wigham, G.; Musila, M.; Kibret, Birhanu A.

doi:10.1029/2021gc009782

Cited by 18 publications

(54 citation statements)

References 135 publications

(335 reference statements)

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“…However, recent tomographic models present no clear evidence for a break in slow wavespeeds (and therefore dynamic support) at the upper mantle depths to which our data are sensitive Emry et al, 2019;Hansen et al, 2012;Kounoudis et al, 2021). Intriguingly, a fast wavespeed band at lithospheric depths in southernmost Ethiopia in the seismic tomographic study of Kounoudis et al (2021) coincident with a broadly (∼500 km-wide) rifted zone (Figure 10) coexists with our zone of absent X. This anomalous region, interpreted by Kounoudis et al (2021) as refractory Proterozoic lithosphere, is not associated with Quaternary volcanism, perhaps resulting in a lack of melt ponding below the region at X depths.…”

Section: East Africacontrasting

confidence: 71%

“…Intriguingly, a fast wavespeed band at lithospheric depths in southernmost Ethiopia in the seismic tomographic study of Kounoudis et al (2021) coincident with a broadly (∼500 km-wide) rifted zone (Figure 10) coexists with our zone of absent X. This anomalous region, interpreted by Kounoudis et al (2021) as refractory Proterozoic lithosphere, is not associated with Quaternary volcanism, perhaps resulting in a lack of melt ponding below the region at X depths. Complex lithospheric seismic structure, both associated with the Kounoudis et al (2021) fast wavespeed band and with the failed Mesozoic Anza rift immediately to the south of it in the Turkana Depression, may be precluding our view of the X.…”

Section: East Africamentioning

confidence: 93%

“…We extend the receiver function (RF) data sets of and Pugh et al (2021) using data recorded up until October 2021 downloaded from the Incorporated Research Institutions for Seismology (IRIS) Data Management System for teleseismic earthquakes with magnitude (M W ) ≥ 5.5 at epicentral distances of 40-90°. We capitalize on the new TRAILS data set in the Turkana Depression (I. D. Bastow, 2019;Ebinger, 2018;Kounoudis et al, 2021) and a further data set in northeast Uganda (Nyblade, 2017) where there is a paucity of station coverage in our RF data set along the East African Rift (EAR). This results in ∼200,000 event-station pairs The inset globe shows the earthquake distribution (green circles) for this study and black circles represent distance intervals of 30° at 30-180° epicentral distance from the center of Africa.…”

Section: Datamentioning

confidence: 99%

“…National borders are marked with thin black lines and countries referred to in text are labeled (COM, Comoros Archipelago including Mayotte; ETH, Ethiopia; KEN, Kenya; MDG, Madagascar; MOZ, Mozambique; and TZA, Tanzania). (b) X-discontinuity vote map (Figure5) plotted above cratons and Cenozoic magmatism adapted fromBegg et al (2009),, andKounoudis et al (2021). Carbonatite volcanoes plotted are ∼45 Ma-recent(Muirhead et al, 2020;Woolley & Kjarsgaard, 2008).…”

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confidence: 99%

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Multigenetic Origin of the X‐Discontinuity Below Continents: Insights From African Receiver Functions

Pugh

Boyce

Bastow

et al. 2023

Geochem Geophys Geosyst

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Mineral phase transitions cause abrupt jumps in local velocity and density structure of the mantle. The seismically observable impedance contrasts resulting from these transitions are termed seismic discontinuities. Due to estimated pressure-temperature dependence of discontinuity depth, the uplift or depression of some global seismic discontinuities can be studied as a thermometer for local mantle structure (e.g., Helffrich, 2000Helffrich, , 2002. On the other hand, nonglobal, localized seismic discontinuities can map the local enrichment of chemical heterogeneity, such that the impedance contrast of the seismic discontinuity renders it seismically observable. One such nonglobal discontinuity at 230-350 km depth is the X-discontinuity (X; e.g., Deuss & Woodhouse, 2004;Revenaugh & Jordan, 1991;Schmerr, 2015) that may be used as a tracer for upper mantle chemical heterogeneity, the distribution of which may shed important insights into mantle dynamics and the extent of chemical equilibration.

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Section: East Africacontrasting

confidence: 71%

Section: East Africamentioning

confidence: 93%

Section: Datamentioning

confidence: 99%

mentioning

confidence: 99%

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Multigenetic Origin of the X‐Discontinuity Below Continents: Insights From African Receiver Functions

Pugh

Boyce

Bastow

et al. 2023

Geochem Geophys Geosyst

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“…For this reason, it is most successful in imaging large magmatic systems associated with large calderas (e.g., Steck et al, 1998;Bai et al, 2020) or continental rifts (e.g. Kounoudis et al, 2021). For a more complete comparison of LET and TST see Thurber (2003).…”

Section: Teleseismic Tomographymentioning

confidence: 99%

Advances in seismic imaging of magma and crystal mush

et al. 2022

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Seismic imaging methods have provided detailed three-dimensional constraints on the physical properties of magmatic systems leading to invaluable insight into the storage, differentiation and dynamics of magma. These constraints have been crucial to the development of our modern understanding of magmatic systems. However, there are still outstanding knowledge gaps resulting from the challenges inherent in seismic imaging of volcanoes. These challenges stem from the complex physics of wave propagation across highly heterogeneous low-velocity anomalies associated with magma reservoirs. Ray-based seismic imaging methods such as travel-time and surface-wave tomography lead to under-recovery of such velocity anomalies and to under-estimation of melt fractions. This review aims to help the volcanologist to fully utilize the insights gained from seismic imaging and account for the resolution limits. We summarize the advantages and limitations of the most common imaging methods and propose best practices for their implementation and the quantitative interpretation of low-velocity anomalies. We constructed and analysed a database of 277 seismic imaging studies at 78 arc, hotspot and continental rift volcanoes. Each study is accompanied by information about the seismic source, part of the wavefield used, imaging method, any detected low-velocity zones, and estimated melt fraction. Thirty nine studies attempted to estimate melt fractions at 22 different volcanoes. Only five studies have found evidence of melt storage at melt fractions above the critical porosity that separates crystal mush from mobile magma. The median reported melt fraction is 13% suggesting that magma storage is dominated by low-melt fraction crystal mush. However, due to the limits of seismic resolution, the seismological evidence does not rule out the presence of small (<10 km3) and medium-sized (<100 km3) high-melt fraction magma chambers at many of the studied volcanoes. The combination of multiple tomographic imaging methods and the wider adoption of methods that use more of the seismic wavefield than the first arriving travel-times, promise to overcome some of the limitations of seismic tomography and provide more reliable constraints on melt fractions. Wider adoption of these new methods and advances in data collection are needed to enable a revolution in imaging magma reservoirs.

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Strain Localization and Migration During the Pulsed Lateral Propagation of the Shire Rift Zone, East Africa

Kolawole

Vick

Atekwana³

et al. 2022

Preprint

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We investigate the spatiotemporal patterns of strain accommodation during multiphase rift evolution in the Shire Rift Zone (SRZ), East Africa. The NW-trending SRZ records a transition from magma-rich rifting phases (Permian-Early Jurassic: Rift-Phase 1 (RP1), and Late Jurassic-Cretaceous: Rift-Phase 2 (RP2)) to a magma-poor phase in the Cenozoic (ongoing: Rift-Phase 3 (RP3)). Our observations show that although the rift border faults largely mimic the pre-rift basement metamorphic fabrics, the rift termination zones occur near crustal-scale rift-orthogonal basement shear zones (Sanangoe (SSZ) and the Lurio shear zones) during RP1-RP2. In RP3, the RP1-RP2 sub-basins were largely abandoned, and the rift axes migrated northeastward (rift-orthogonally) into the RP1-RP2 basin margin, and northwestward (strike-parallel) ahead of the RP2 rift-tip.The northwestern RP3 rift-axis side-steps across the SSZ, with a rotation of border faults across the shear zone and terminates further northwest at another regional-scale shear zone. We suggest that over the multiple pulses of tectonic extension and strain migration in the SRZ, pre-rift basement fabrics acted as: 1) zones of mechanical strength contrast that localized the large rift faults, and 2) mechanical 'barriers' that refracted and possibly, temporarily halted the propagation of the rift zone. Further, the cooled RP1-RP2 mafic dikes facilitated later-phase deformation in the form of border fault hard-linking transverse faults that exploited mechanical anisotropies within the dike clusters and served as mechanically-strong zones that arrested some of the RP3 fault-tips. Overall, we argue that during pulsed rift propagation, inherited strength anisotropies can serve as both strain-localizing, refracting, and transient strain-inhibiting tectonic structures.

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Body‐Wave Tomographic Imaging of the Turkana Depression: Implications for Rift Development and Plume‐Lithosphere Interactions

Cited by 18 publications

References 135 publications

Multigenetic Origin of the X‐Discontinuity Below Continents: Insights From African Receiver Functions

Multigenetic Origin of the X‐Discontinuity Below Continents: Insights From African Receiver Functions

Advances in seismic imaging of magma and crystal mush

Strain Localization and Migration During the Pulsed Lateral Propagation of the Shire Rift Zone, East Africa

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