Abstract
AbstractMagmatic intrusions play a vital role not only in accommodating extensional stresses in continental rifts but also in feeding volcanic systems. The location, orientation, and timescale of dike intrusions are dictated by the interaction of regional and local stresses, the effect of pre‐existing weaknesses, and the composition of magma. Observing active intrusions can provide important information regarding the interaction between magmatic processes and the tectonic stress field during continental rifting. We focus on a seismic swarm that occurred in 2015 to the northeast of Fentale volcano, in the Main Ethiopian Rift (MER), and use radar interferometry to study surface deformation associated with the seismic swarm. Interferograms show a pattern of dike‐induced deformation, with a model estimate of volume change of 33×106±0.6×106m3 at a depth range of 5.4 to 8 km. We use a small baseline subset algorithm to calculate line of sight time series and find that the displacements decay exponentially with a decay constant of ∼83 days. Coupled source‐sink models suggest that such slow dike intrusions require a high viscosity rhyolitic magma. The difference in behavior between Fentale and other caldera systems in the MER, which show multi‐year cycles of inflation and deflation, suggests fundamental differences in magma composition and architecture of the plumbing system. This is the first direct observation of a dike intrusion in the MER and provides new constraints on the temporal‐spatial patterns of stress and strain that occur during continental rifting. Whether this activity is transient or a long‐term feature associated with rift evolution is an open question.
Highlights
The stress accumulated along divergent plate boundaries can be accommodated by dyke-driven rifting episodes [Ayele et al, 2007, 2009; Wright et al, 2012; Ebinger et al., 2013]
Dyke intrusions play a vital role in accommodating strain and have a significant impact on the rheology of the continental crust during rifting
Elastic models of InSAR data show that the dyke is ∼6±1 km long, ∼2±0.2 m wide, with a depth range of 5.4 km to 8 km from the surface
Summary
We report the first directly detected dyke intrusion to occur in the Main Ethiopian. The dyke-induced deformation decayed exponentially (τ= 83 days) consistent with a relatively high viscosity peralkaline rhyolite magma. Magmatism in the Northern MER is currently tectonically controlled in contrast to caldera-wide deformation in the Central MER. This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination–1–and proofreading process which may lead to differences between this version and the Version of Record.
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