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Continental breakup, tbe final stretch: seismic reflection and borehole evidence from the Danakil Depression, Ethiopia

Author(s): Ian Bastow Imperial College, London, United Kingdom
Adam Booth
Derek Keir
Giacomo Corti
Craig Magee
John Warren
Jason Wilkinson
Jason Wilkinson

During continental breakup, the locus of strain shifts from a broad zone of border faulting and ductile plate stretching to a narrow zone of magma intrusion in a young ocean basin: a mid-ocean ridge. Recent studies of rifts and margins worldwide suggest that the shift to magmatic extension occurs sub-aerially, prior to the onset of seafloor spreading, We explore this hypothesis using recently-acquired seismic reflection data and accompanying borehole geological constraints from the Dallal basin of the Danakil Depression, northernmost Ethiopia: a unique region of incipient transition from continental rifting to incipient oceanic spreading, Our data reveal thick sequences of evaporites deposited in an asymmetric basin, whose subsidence has been controlled primarily by a major, east dipping normal fault Surprisingly, no significant magmatism is observed in the upper ~1000 km. Age constraints on the potash-bearing sequence being mined in the basin demonstrate that Dallol's thick evaporate sequences have been deposited in the last several tens-to-hundreds of thousands of years. Basin formation cannot be easily attributed to the effects of magmata intrusion. Instead, an abrupt, localized, late-stage plate-stretching phase marks the final stages of breakup, prior to the onset of seafloor spreading. It is unclear whether the localized stretching is due to heating and weakening of the plate by protracted dyke intrusion, or whether strong, flanking lithosphere of the Nubian plateau and the Danakil micro-plate control the focusing. Regardless, the magmatic locus of strain, developed during the final stages of breakup, may not necessarily represent the final break-up boundary and ultimate spreading center location.

Continental breakup, the final stretch: seismic reflection and borehole evidence from the Danakil Depression, Ethiopia
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