Seismic Migration Imaging of the Lithosphere beneath Afar Rift, East Africa
Date Issued
2015
Date
2015
Author(s)
Lee, Timothy Ting-Yu
Abstract
Different plate boundaries are characterized by the way the plates move relative to each other. One kind of plate boundaries is divergent boundary, which occurs where two plates slide apart. At zones of continent-to-continent rifting, divergent boundaries will be where the new ocean basin forms as the continents split, accompanied by volcanic activities and earthquakes. The origin of divergent boundaries are thought to be associated with heating and stretching in the lithosphere. The Afar Rift system in east Africa is an ideal natural laboratory for investigating the process of divergent boundary and incipient continental rifting. It is located at the triple junction of three rifts, Southern Red Sea Rift (RSR), GOA (Gulf of Aden Rift) and MER (Main Ethiopian Rift), and the ongoing continental breakup at Afar transitions to seafloor spreading toward the southern Red Sea. Previous studies favor the explanation that Afar is influenced by a mantle plume that weakens the lithosphere through thermal erosion and magma infiltration. However, the location and degree of plume influence are debated. In this study, recordings of seismic array at Afar are used to produce the first high-resolution seismic images from scattered wavefield of Afar lithosphere, to detect upper-mantle discontinuities. We reveal two seismic discontinuities on the north and south section of our 2-D profile, centered between the north-western Afar and Ethiopia Plateau and between the south-western Afar and Main Ethiopian Rift. The discontinuity in the south is identified at ~75 km depth characterized by a pronounced velocity reduction, which may be interpreted as the lithosphere-asthenosphere boundary (LAB) or as velocity contrast enhanced by hot mantle upwelling. The other discontinuity to the north dips southward from 70 to 90 km depth, characterized by a velocity increase with depth, in contrast with the observation in the south. Our study shows evidence that the Afar lithosphere is likely modified by thermal effect in the uppermost mantle, where the presence of mantle plume cannot be excluded.
Subjects
Africa
Afar
rift
depression
triple junction
seismic migration
upper-mantle
lithosphere
discontinuity
Type
thesis
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