Crustal structure across the São Miguel Island (Azores, North Atlantic) and tectonic implications

• Published in: Marine geophysical researches 2022-12, Vol.43 (4), p.1-17, Article 41
• Main Authors: Batista, L., Hübscher, C., Terrinha, P., Matias, L., Afilhado, Alexandra, Loureiro, A., Weiß, B.
• Format: Article
• Language: English
• Subjects: Azores Plateau; Concretions; Crustal structure; Deformation; Earth and Environmental Science; Earth Sciences; Geophysics/Geodesy; Graben; Isotopes; Landslides; Mass transport; Moho; Oceanography; Offshore Engineering; Original Research Paper; P-waves; Plastic flow; Plate boundaries; Reflection; Seismic profiles; Seismic reflection profiles; Seismic velocities; Seismic wave velocities; Seismicity; Terceira rift; Underplating; Uplift; Wave velocity
• ISSN: 0025-3235; 1573-0581
• DOI: 10.1007/s11001-022-09503-y

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 refection seismic profle across the island and the Terceira Rift along with multichan nel seismic refection profles 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 defned 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 flled in with 1500 m of sediments and various mass transport deposits. The São Miguel Deep Ductile Deformation Zone is considered as a difuse plate boundary where deformation is accommodated by brittle mechanisms (seismicity) and plastic fow (lateral thickness variation of the lower crust).