Rift structure, development and fault activity at high resolution using geophysical and drilling data analysis: the Corinth Rift, Greece and Danakil Rift, East Africa

Abstract

Continental rifting plays a fundamental role in the Wilson tectonic cycle, enabling the final break-up of continents and the initiation of seafloor spreading. However, very little high-resolution comparative analysis of faulting at magma-rich and magma-poor contemporary rifts has been conducted, with previous studies focusing on passive margins. Therefore, using high-resolution geophysical and drilling data we have analysed the rift structure, development and fault activity at the active Corinth Rift, Greece (magma-poor) and Danakil Rift, East Africa (magma-rich). Quantitative analysis of >500 rift axis faults, identified in the Danakil Depression using remote sensing, shows faulting is more significant towards rift ends, away from magmatic segments. Seismic reflection and borehole data shows that ~30% of crustal extension is accommodated by axial faulting in areas of low magmatism, highlighting the importance of faulting in the final stages of magma-rich rifting. Across the Corinth Rift, new 2D seismic data (Petromaks Deep Rift Project) combined with well data from IODP Expedition 381, has enabled increased fault throw rates over the last 12 kyrs compared with last 130 kyrs, to be identified for both major border and minor intra-rift faults. Flexure in the Corinth Rift centre caused by subsidence on the border fault hanging walls, may have created a network of minor intra-rift faults which can accommodate up to 50% of extension. We compared the contribution of seismic (brittle faulting) and aseismic deformation in accommodating extension in both rifts by calculating the seismic moment to geodetic moment rate ratio (S/G). The Corinth Rift has a higher S/G (0.43) than the Danakil Depression (0.03), indicating greater amounts of extension are accommodated by brittle faulting in the magma-poor rift. S/G variations within each rift highlights variation in the contribution of the extension accommodating mechanisms. Relatively high S/G (~0.1) in the north Danakil Depression indicates that brittle faulting accommodates a significant amount of extension in this area, despite being in the final stages of magma-rich break-up. Relatively low S/G (~0.1-0.15) in the western Corinth Rift supports significant aseismic deformation occurring here, potentially on a low angle detachment at depth. The findings of this thesis show that faulting is important in both magma-rich and magma-poor rifts, with analysis showing that intra-rift fault networks play an important role accommodating extension in both types of rift. In the Danakil Depression, faulting is most prominent at segments ends, compared with cumulative fault displacement being highest in the Corinth Rift centre.

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Identifiers

ORCID for Gareth Lloyd Hurman: orcid.org/0000-0002-5287-1196

ORCID for Lisa Mcneill: orcid.org/0000-0002-8689-5882

ORCID for Derek Keir: orcid.org/0000-0001-8787-8446

ORCID for Jonathan Bull: orcid.org/0000-0003-3373-5807

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