Seismic anisotropy of the lithosphere/asthenosphere system beneath the Rwenzori region of the Albertine Rift

Homuth, Benjamin; Löbl, U.; Batte, Arthur; Link, Klemens; Kasereka, C. M.; Rümpker, Georg

doi:10.1007/s00531-014-1047-0

Cited by 13 publications

(15 citation statements)

References 45 publications

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“…Many (~60%) of the stations used in this study are located in the East African Rift. Previous shear‐wave splitting studies in this region (Homuth et al, ; Gao et al, ; Bagley & Nyblade, ; Tepp et al, ) have shown that apparent splitting varies strongly both spatially and with backazimuth. This leads to the conclusion that anisotropy in the upper mantle beneath the East African Rift is highly complex, with strong lateral variation and multiple layers of anisotropy.…”

Section: Interpretation Of Splitting Discrepanciesmentioning

confidence: 82%

Lowermost Mantle Anisotropy Beneath Africa From Differential SKS‐SKKS Shear‐Wave Splitting

2019

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We investigate seismic anisotropy in the lowermost mantle in the vicinity of the African large low shear velocity province (LLSVP) using observations of differential SKS‐SKKS shear‐wave splitting. We use data from 375 permanent and temporary stations in Africa which enable us to map the spatial distribution of the anisotropic regions of the lowermost mantle in unprecedented detail. Our results corroborate previous findings that anisotropy is most clearly observed at the margins of the LLSVP, indicating strong deformation at its border, and they are generally consistent with a mostly isotropic LLSVP interior. We find that most discrepant SKS‐SKKS measurements sample the lowermost mantle close to what is inferred to be the root of the Afar plume. We also identify strongly discrepant splitting in the vicinity of a previously mapped ultralow velocity zone (ULVZ) at the base of the LLSVP, beneath Central Africa. This represents an unusual observation of lowermost mantle anisotropy that is spatially coincident with a ULVZ and may reflect a unique anisotropic mechanism such as alignment of partial melt or the presence of strongly anisotropic magnesiowüstite. We interpret discrepant measurements outside of the LLSVP as likely reflecting a change in flow direction from the horizontal plane to a more vertical direction, which may be caused by deflection at the steep LLSVP border. We propose that our observations of D″ anisotropy associated with the African LLSVP can be explained by a mantle flow regime that maintains passive thermochemical piles with slab‐driven flow and allows for the formation of upwellings at their edges.

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Section: Interpretation Of Splitting Discrepanciesmentioning

confidence: 82%

Lowermost Mantle Anisotropy Beneath Africa From Differential SKS‐SKKS Shear‐Wave Splitting

2019

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“…The blue and red lines denote SC and RC methods, respectively, from this study. Other lines denote splitting results from Gao et al () (dark red), Bagley and Nyblade () (green), Albaric et al () (yellow), and Homuth et al () (dark blue). Line length is proportional to the weighted average delay time for this study and the published delay time for the other studies.…”

Section: Discussionmentioning

confidence: 94%

“…Fast directions parallel rift border faults and have an average delay time of about 1 s. Splitting measurements from local mantle earthquakes are nearly an order of magnitude higher than those of co‐located lower crustal earthquakes, indicating that the mantle is the dominant contributor to the observed anisotropy. Finite‐frequency waveform modeling shows that the rift‐parallel fast polarizations are consistent with horizontal transverse isotropy, interpreted as rift‐parallel magmatic intrusions or lenses located within the lithospheric mantle (Homuth et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…In some areas, the mantle plume transfers heat, magma, and volatiles to the African plate, changing its composition and structure over time (e.g., Bastow & Keir, 2011;Ebinger & Sleep, 1998;Lee et al, 2016). Although several regional and local studies establish a strong context for depth distribution and spatial variations in mantle anisotropy beneath northeastern Africa (e.g., Ayele et al, 2004;Gashawbeza et al, 2004;Hammond et al, 2014;Kendall et al, 2006), anisotropy patterns in the weakly magmatic Western rift sector of the EARS are only loosely constrained by widely spaced arrays in the region (Bagley & Nyblade, 2013;Walker et al, 2004;Yu et al, 2015), a high resolution rift transect in the southern Malawi rift (Reed et al, 2017), and by a dense array in southwestern Uganda (Homuth et al, 2016). We analyze seismic anisotropy patterns beneath the southern Tanganyika, Rukwa, and northern Malawi rift zones using two independent temporary seismic arrays, SEGMeNT (Shillington et al, 2016) and TANGA14 (Hodgson et al, 2017;Figures 2, S1, and S2 in the supporting information).…”

Section: Introductionmentioning

confidence: 99%

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Seismic Anisotropy of the Upper Mantle Below the Western Rift, East Africa

et al. 2018

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Although the East African rift system formed in cratonic lithosphere above a large‐scale mantle upwelling, some sectors have voluminous magmatism, while others have isolated, small‐volume eruptive centers. We conduct teleseismic shear wave splitting analyses on data from 5 lake‐bottom seismometers and 67 land stations in the Tanganyika‐Rukwa‐Malawi rift zone, including the Rungwe Volcanic Province (RVP), and from 5 seismometers in the Kivu rift and Virunga Volcanic Province, to evaluate rift‐perpendicular strain, rift‐parallel melt intrusion, and regional flow models for seismic anisotropy patterns beneath the largely amagmatic Western rift. Observations from 684 SKS and 305 SKKS phases reveal consistent patterns. Within the Malawi rift south of the RVP, fast splitting directions are oriented northeast with average delays of ~1 s. Directions rotate to N‐S and NNW north of the volcanic province within the reactivated Mesozoic Rukwa and southern Tanganyika rifts. Delay times are largest (~1.25 s) within the Virunga Volcanic Province. Our work combined with earlier studies shows that SKS‐splitting is rift parallel within Western rift magmatic provinces, with a larger percentage of null measurements than in amagmatic areas. The spatial variations in direction and amount of splitting from our results and those of earlier Western rift studies suggest that mantle flow is deflected by the deeply rooted cratons. The resulting flow complexity, and likely stagnation beneath the Rungwe province, may explain the ca. 17 Myr of localized magmatism in the weakly stretched RVP, and it argues against interpretations of a uniform anisotropic layer caused by large‐scale asthenospheric flow or passive rifting.

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“…Seismological data, (Homuth et al, 2016;Wölbern et al, 2010) shows the absence of a crustal root and thinned crust below the Rwenzori Mountains. On the basis of microtectonic measurements and focal mechanism analysis, the tectonic setting of the Rwenzori Mountains is assumed to be dominated by strike-slip movements (e.g.…”

Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%

Deformation and sedimentary evolution of the Lake Albert Rift (Uganda, East African Rift System)

Simon

Guillocheau

Robin

et al. 2017

Marine and Petroleum Geology

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This study proposed a new reconstruction of the tectono-sedimentary evolution of the Lake Albert Rift based on a biostratigraphical, sedimentological and structural re-evaluation of the outcropping data and on an exceptional subsurface dataset.The infilling of the rift consists of lacustrine deposits wherein two major unconformities dated at 6.2 Ma and 2.7 Ma were characterized, coeval with major subsidence and climatic changes.Combined with the fault analysis, the evolution and distribution of the subsidence highlights a foursteps evolution of the rift after its initiation dated at 17.0 Ma.The first phase (17.0 -6.2 Ma) consists of low and diffuse extension associated with low accommodation rates ranging from 150 to 200 m/Ma. Restricted in the southern part of the basin, the depocenter location is poorly controlled by faults, meaning that the basin extension was potentially larger at this time.The second time interval (6.2 -2.7 Ma) shows an increase of accommodation rates with values reaching more than 800 m/Ma. These high rates combined with the location of the major depocenters down the bounding faults argue for a first true rifting phase.Between 2.7 Ma and 0.4 Ma, the accommodation rates decreases to reach less than 400 m/Ma and the individualization of major depocenters continue down the major fault in the southern, and northwestern parts of the basin.

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Seismic anisotropy of the lithosphere/asthenosphere system beneath the Rwenzori region of the Albertine Rift

Cited by 13 publications

References 45 publications

Lowermost Mantle Anisotropy Beneath Africa From Differential SKS‐SKKS Shear‐Wave Splitting

Lowermost Mantle Anisotropy Beneath Africa From Differential SKS‐SKKS Shear‐Wave Splitting

Seismic Anisotropy of the Upper Mantle Below the Western Rift, East Africa

Deformation and sedimentary evolution of the Lake Albert Rift (Uganda, East African Rift System)

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