Abstract
The crustal and uppermost lithospheric mantle of the São Miguel Island in the Azores Plateau was investigated using one 160 km long refraction and wide angle reflection seismic profile across the island and the Terceira Rift along with multichannel seismic reflection profiles on the top of it. P-wave velocity model shows that São Miguel Island is made up of 5 crustal layers. The sedimentary sequence varies between 150 and 1500 m of thickness and the upper and lower crusts vary from 6 km to maximum thickness of > 10 km altogether. The Moho discontinuity lies at 15 km of depth underneath the island and at 11 km outside the island and rift. A 125 km-long layer with a maximum thickness of 2.5 km and Vp of 7.6 km/s is defined at the base of the crust. We speculate that this lens-shaped layer consists of gabbro cumulates formed by magmatic underplating. Extensional southwards directed simple shear across the whole crust and the Moho discontinuity – São Miguel Deep Ductile Deformation Zone – causes uplift, northwards tilting of the island and landslides. Decoupling between ductile deformation in depth and brittle deformation in the shallow levels caused the formation of a rift half-graben filled in with 1500 m of sediments and various mass transport deposits. The São Miguel Deep Ductile Deformation Zone is considered as a diffuse plate boundary where deformation is accommodated by brittle mechanisms (seismicity) and plastic flow (lateral thickness variation of the lower crust).
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Acknowledgements
We sincerely thank Captain Thomas Wunderlich and his crew of RV Meteor for their support during the M79/2 cruise. This project was supported by German Research Foundation (DFG, grant Hu698/19 − 1). Luis Batista thanks FCT for the PhD grant SFRH/BD/81,351/2011. The support of Landmark Graphics Corporation via the Landmark University Grant Program is also acknowledged. The manuscript benefitted from valuable comments by editor Wu-Cheng Chi and the reviews by Philippe Schnürle and an anonymous reviewer.
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This work was supported by Portuguese national funding agency for science, research and technology (FCT) (grant SFRH/BD/81351/2011) and by German Research Foundation (DFG, grant Hu698/19-1). The authors have no relevant financial or non-financial interests to disclose.
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LB: Conceptualization, Methodology, Investigation, Validation, Writing-Original Draft. CH: Funding acquisition, Resources, Supervision, Writing-Review and Editing. PT: Funding acquisition, Investigation, Supervision, Writing-Original Draft. LM: Geophysical modelling, Software, Writing-Review and Editing. AA: Software, Validation, Data Curation. AL: Error analysis, validation, Data Curation. BW: Resources; Data Curation
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Batista, L., Hübscher, C., Terrinha, P. et al. Crustal structure across the São Miguel Island (Azores, North Atlantic) and tectonic implications. Mar Geophys Res 43, 41 (2022). https://doi.org/10.1007/s11001-022-09503-y
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DOI: https://doi.org/10.1007/s11001-022-09503-y