The crust-mantle transition beneath the Azores region (central-north Atlantic Ocean)

The Azores region straddles the Mid-Atlantic Ridge and comprises volcanic islands and seamounts interspersed with nonmagmatic oceanic basins arranged along subparallel slow-spreading systems. The cross-check of CO2- rich fluid inclusions barometry from lavas and tephras erupted during the last 20 ka with the sources of seismicity of the last 22 years traced the deepest magma accumulation zone at a regional scale. These zones are considered to represent the boundary between the dense rocks of magma systems and the lithospheric mantle. This boundary is at a depth range of similar to 17 to 20 km beneath the islands close to the Mid-Atlantic Ridge, which are younger than 500 ka, and up to similar to 29.4 km beneath the eastern island of S. Miguel, younger than 800 ka and the nearby Dom Joao de Castro Seamount and the Hirondelle Basin. The same method has been applied to the similar to 2 Ma-old volcanic products of Flores, the similar to 1.9 Ma old S. Jorge and the 5 Ma-old lavas of Santa Maria. Results revealed a depth of similar to 30.5 km beneath the Flores and similar to 26 km beneath the similar to 1.9 Ma-old S. Jorge. These two islands are west and east of the Mid-Atlantic Ridge, within 200 km. Finally, the crust-mantle transition has been found below Santa Maria, the easternmost island, similar to 500 km away from the Mid-Atlantic Ridge at a depth of similar to 33 km. Overall, repeated mafic magma injections at the base of each magma system generated vertically stacked layered ultramafic mush bodies, which thickened the crust overtime.

Automated summary

The Azores region is made up of volcanic islands and seamounts located on the Mid-Atlantic Ridge. The deepest magma accumulation zone has been identified using CO2-rich fluid inclusions barometry and seismicity analysis. This zone represents the boundary between magma systems and the lithospheric mantle. Repeated mafic magma injections have resulted in thickening of the crust over time.