Seismic Imaging of Dante's Domes Oceanic Core Complex From Streamer Waveform Inversion and Reverse Time Migration.

Early arrival traveltime tomography and full waveform inversion were conducted on downward continued streamer seismic data at Dante's Domes oceanic core complex (OCC), providing unprecedented details of shallow P wave velocity structure. Together with reverse time migration images, seafloor morphology, in situ geological samples, magnetic and gravity data, the seismic constraints are used to infer the lithological distribution along the seismic profiles. Based on the striking similarity in velocity structure beneath the corrugated domes with other OCCs and drilling results from Atlantis Massif, we confidently reconfirmed the Southern Dome as dominantly gabbroic rocks, and the Northern Dome as serpentinized peridotites. A series of isolated gabbroic bodies embedded in the diabase and basaltic layers is observed in the breakaway zone, suggesting that the initiation of Dante's Domes OCC occurred over a long period during which there were several failed attempts to form a long‐lived detachment fault. This early development of the OCC probably occurred under a regime of alternating magma starvation and magma replenishment. The predominantly gabbroic section, beneath the Southern Dome and extending to termination, indicates the OCC has been created with relatively high magma flux. We also imaged distinct shallow subseafloor reflections which are also termed as D reflectors underneath the corrugated domes. The location of the D reflectors is similar to those in the Atlantis Massif, with depths well correlated with the top of exhumed gabbroic bodies and the discontinuities in the D reflectors between gabbroic bodies. Our findings contribute to the understanding of processes controlling the OCCs initiation and evolution at slow spreading ridges. Plain Language Summary: The lithospheric structure generated along the mid‐ocean ridges is determined by the magmatic accretion and tectonic extension, the spatiotemporal variation of which generally depends on the spreading rates. Along slow spreading ridges, tectonic extension dominates and sometimes forms oceanic core complexes (OCCs) generated by heterogeneous exhumed lower crustal and upper mantle section caused by long‐lived, large‐offset detachment faults. The Dante's Domes OCC, located between 26°32′N and 26°40′N on the African plate along the Mid‐Atlantic Ridge, was created by a ∼18‐km‐long detachment fault. Here detailed structural variability within the Dante's Domes OCC was obtained from advanced seismic imaging techniques. The lithological distribution interpreted from seismic imaging, which could be employed to infer magmatic accretion and tectonic extension behaviors, improved our understanding of the initiation and evolution of Dante's Domes OCC. A series of linear ridges are interpreted as breakaways where the OCC initiated, suggesting that the Dante's Domes OCC experienced several failed attempts to form long‐lived detachment fault, and was not exhumed quickly as previously postulated. Key Points: Detailed structure of Dante's Domes oceanic core complex (OCC) was obtained from downward continued streamer waveform inversion and reverse time migrationA series of narrow ridges interpreted as breakaways indicates that the initiation of Dante's Domes OCC was not fast as previously postulatedVelocity contrasts of the shallow low‐velocity and fractured layer and deeper high‐velocity gabbros contributes to the shallow reflectivity [ABSTRACT FROM AUTHOR]