Tectonic, Volcanic and Geothermal Processes in a Continental Rift

  • Tesfaye T Tessema

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Continental rifting is attributed to faulting and magmatism at variable depth and scale. As the rift develops, the crustal strain migrates from border faults to the rift-floor eventually leading to the formation of new ocean basins. The velocity field and strain rates are key observables needed to understand present-day rift activity. Magmatic segments and volcanic centres are associated with geothermal resources that can contribute to the development of green energy.

In this thesis, I use Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) observations: (1) to examine and quantify the current velocity field and strain rate distribution of a continental rift using the Main Ethiopian Rift (MER) as a case example, (2) to understand the timescale and rheology of dyking in continental rifting and (3) to examine the temporal-spatial variability of surface deformation in a geothermal prospect area and the underlying source mechanism.

In continental rifting, magmatism and faulting determine the distribution and magnitude of strain. Here, I use geodetic observations to calculate the combined velocity field and strain rate over the MER. A high velocity gradient is observed across the rift-floor and a decrease in rate of separation of Nubia-Somalia from north to south. A high normal strain rate is observed in the rift-floor, but the atmospheric residual biased the signals on the plateaus. Dyke intrusion is an important mechanism of strain accommodation during magmatic rifting and the timescale of intrusion can provide insight into crustal rheological properties and magma composition. I describe here the first direct observation of dyke intrusion in the MER. The ground deformation shows exponential decay over 3 months consistent with a high viscosity peralkaline rhyolitic magma. Magmatic rifts provide a source of heat for shallow hydrothermal systems. I identify two regions that show subsidence at the Tendaho geothermal prospect, central Afar. The deformation started mid-2008 and the pattern is consistent with the aggregate effect of a deep magmatic source and shallow hydrothermal or agricultural activity.

Together, these geodetic observations reveal the spatially and temporally variable distribution of strain during continental rifting. The variability in mechanism of surface deformation along the rift-axis suggests fundamental differences in the behaviour and architecture of the plumbing systems. These observations illustrate the spatial-temporal patterns of strain that occur prior to continental breakup. The new measurements will be valuable for seismic hazard assessment and resource identification in the region.
Date of Award24 Jun 2021
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorJuliet J Biggs (Supervisor) & Michael Kendall (Supervisor)

Keywords

  • Tectonic deformation
  • InSAR
  • GNSS
  • Dyke
  • Geothermal
  • Subsidence
  • East African Rift System
  • Main Ethiopian Rift
  • Strain rates
  • Peralkaline rhyolite

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