TY - JOUR
T1 - Body-Wave Tomographic Imaging of the Turkana Depression
T2 - Implications for Rift Development and Plume-Lithosphere Interactions
AU - Kounoudis, R.
AU - Bastow, I. D.
AU - Ebinger, C. J.
AU - Ogden, C. S.
AU - Ayele, A.
AU - Bendick, R.
AU - Mariita, N.
AU - Kianji, G.
AU - Wigham, G.
AU - Musila, M.
AU - Kibret, B.
N1 - Publisher Copyright:
© 2021. The Authors.
PY - 2021/8
Y1 - 2021/8
N2 - The Turkana Depression, a topographically subdued, broadly rifted zone between the elevated East African and Ethiopian plateaus, disrupts the N–S, fault-bounded rift basin morphology that characterizes most of the East African Rift. The unusual breadth of the Turkana Depression leaves unanswered questions about the initiation and evolution of rifting between the Main Ethiopian Rift (MER) and Eastern Rift. Hypotheses explaining the unusually broad, low-lying area include superposed Mesozoic and Cenozoic rifting and a lack of mantle lithospheric thinning and dynamic support. To address these issues, we have carried out the first body-wave tomographic study of the Depression's upper mantle. Seismically derived temperatures at 100 km depth exceed petrological estimates, suggesting the presence of mantle melt, although not as voluminous as the MER, contributes to velocity anomalies. A NW–SE-trending high wavespeed band in southern Ethiopia at (Formula presented.) 200 km depth is interpreted as refractory Proterozoic lithosphere which has likely influenced the localization of both Mesozoic and Cenozoic rifting. At (Formula presented.) 100 km depth below the central Depression, a single localized low wavespeed zone is lacking. Only in the northernmost Eastern Rift and southern Lake Turkana is there evidence for focused low wavespeeds resembling the MER, that bifurcate below the Depression and broaden approaching southern Ethiopia further north. These low wavespeeds may be attributed to melt-intruded mantle lithosphere or ponded asthenospheric material below lithospheric thin-spots induced by the region's multiple rifting phases. Low wavespeeds persist to the mantle transition zone suggesting the Depression may not lack mantle dynamic support in comparison to the two plateaus.
AB - The Turkana Depression, a topographically subdued, broadly rifted zone between the elevated East African and Ethiopian plateaus, disrupts the N–S, fault-bounded rift basin morphology that characterizes most of the East African Rift. The unusual breadth of the Turkana Depression leaves unanswered questions about the initiation and evolution of rifting between the Main Ethiopian Rift (MER) and Eastern Rift. Hypotheses explaining the unusually broad, low-lying area include superposed Mesozoic and Cenozoic rifting and a lack of mantle lithospheric thinning and dynamic support. To address these issues, we have carried out the first body-wave tomographic study of the Depression's upper mantle. Seismically derived temperatures at 100 km depth exceed petrological estimates, suggesting the presence of mantle melt, although not as voluminous as the MER, contributes to velocity anomalies. A NW–SE-trending high wavespeed band in southern Ethiopia at (Formula presented.) 200 km depth is interpreted as refractory Proterozoic lithosphere which has likely influenced the localization of both Mesozoic and Cenozoic rifting. At (Formula presented.) 100 km depth below the central Depression, a single localized low wavespeed zone is lacking. Only in the northernmost Eastern Rift and southern Lake Turkana is there evidence for focused low wavespeeds resembling the MER, that bifurcate below the Depression and broaden approaching southern Ethiopia further north. These low wavespeeds may be attributed to melt-intruded mantle lithosphere or ponded asthenospheric material below lithospheric thin-spots induced by the region's multiple rifting phases. Low wavespeeds persist to the mantle transition zone suggesting the Depression may not lack mantle dynamic support in comparison to the two plateaus.
KW - East Africa
KW - Turkana Depression
KW - continental rifting
KW - seismic tomography
KW - upper mantle structure
UR - http://www.scopus.com/inward/record.url?scp=85113743533&partnerID=8YFLogxK
U2 - 10.1029/2021GC009782
DO - 10.1029/2021GC009782
M3 - Article
AN - SCOPUS:85113743533
SN - 1525-2027
VL - 22
JO - Geochemistry, Geophysics, Geosystems
JF - Geochemistry, Geophysics, Geosystems
IS - 8
M1 - e2021GC009782
ER -