Intraplate Lithospheric Deformation and the Formation of a Large Volcanic Regions

Abstract

Large igneous systems are formed either in areas of thin lithosphere at or near plate boundaries or by mantle-melting anomalies in intraplate settings with comparatively thicker lithosphere. At plate boundaries extension-driven decompression melting or flux melt due to slab-derived materials dominate. Intraplate magmatism is associated to thermal or compositional anomaly in the mantle. Even though many 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 appears easily explained by the evolution of a semi-stable mantle-melting anomaly. We present seismic data collected in 2022 across the Madeira-Tore Rise that show that the extended volcanic region may be related to lithospheric-scale intraplate deformation. The ~1000 km long region displays a broad bathymetric swell (Rise) and abundant volcanic constructions of different dimensions across a several-hundreds-km wide swath. The origin of the rise and volcanic constructions is unclear. The rise has often being associated to excess magmatism and formation of thicker-than normal oceanic crust for a few-million-years period during the Cretaceous. This magmatic event is loosely associated to the seafloor-spreading magnetic lineation named as the J-anomaly, and the rise is often referred as the J-anomaly ridge. However, when analysed in detail, the magnetic J-anomaly is not located at the rise, but to east, and the presence of a basement ridge that may explain the swell has not being yet proved. We show that the seafloor rise is not is underlaid by thin crust, and thicker crust is located to the east, coincident with magnetic J-anomaly. Seismic images display regional-scale tilting of strata covering the oceanic plate, and local contractional deformation. The images show brittle faulting associated to deformation creating some of largest seamounts in the area by tectonic uplift of several km. We propose that the ~1000 km long and ~200 km wide Madeira-Tore Rise volcanism possibly has formed associated to lithospheric-scale faults linking the asthenosphere to the surface providing long term conduits