Intraplate Lithospheric Deformation Forms Large Volcanic Regions

Large igneous systems form either in areas of thin lithosphere at or near plate boundaries or by mantle-melting anomalies in intraplate settings with comparatively thicker lithosphere. Decompression melting or flux melt dominate at plate boundaries. Intraplate magmatism relates to thermal or compositional anomaly in the mantle. Although questions remain open, our understanding of the fundamental driving processes of these systems has dramatically improved during the last 50 years. However, some intraplate large volcanic regions display a complex distribution of magmatic activity that spans a large age range and does not appear easily explained by semi-stable mantle-melting anomalies. 

The Madeira-Tore Rise (MTR) is often associated to excess magmatism forming thick oceanic crust at Cretaceous time. However, the ~1000 km long MTR broad bathymetric swell contains numerous individual volcanic constructions of different dimensions and age, across a hundreds-of-km wide swath. The MTR and volcanic constructions origin is unclear. The MTR magmatic event is inferred to be associated to the seafloor-spreading magnetic lineation named the J-anomaly, and the MTR is often referred as J-anomaly ridge. However, when analysed in detail, the magnetic J-anomaly is located east of the rise. Many volcanoes are inferred hot-spot related.

Seismic data collected in 2018 & 2022 show that the basement ridge of the MTR swell is unrelated to thick crust but to long-wavelength lithospheric flexure. The lithospehre deformation is expressed by folding, faultiong and large-scale tilting indicated by regional angular stratigraphical uncorformities. The spatial and temporal coincident of deformation with the MTR volcanic region support that long-lived volcanism may be related to lithospheric-scale intraplate deformation unrelated to hot spot activity.