New Late Cretaceous and CAMP Magmatic Sources off West Iberia, From High-Resolution Magnetic Surveys on the Continental Shelf

Magma-poor rifted margins can be affected by magmatic occurrences coeval with rifting and post-rifting. Understanding the geological processes that originated these magmatic events requires determining their extent, type and size of magmatic bodies and tectonics. This work investigates the distribution and origin of two large magmatic events off SW Iberia, the Late Triassic Central Atlantic Magmatic Province (CAMP) and the West Iberia Late Cretaceous Alkaline Province (WILCAP). Marine magnetic data were densely acquired over similar to 4,400 km(2) and new magnetic maps reveal a complex heterogeneous anomaly field with different anomaly zones. A wide number and variety of magmatic bodies are interpreted, from km-scale deeply intruded plutons to small plug-like and dike-like intrusions. Integration with bathymetry and seismic reflection data allows discussing the geometry, extent and age of the magmatic sources. The Cabo Raso complex is a densely intruded zone related to the WILCAP event. The Sines complex comprises the offshore prolongation of the on-land Sines WILCAP magmatic rocks but also the newly mapped Covo and Milfontes anomalies. Covo is possibly the largest magmatic intrusion recognized in West Iberia. Milfontes intrudes the non-rifted Paleozoic crust and is the first known evidence of a plutonic source of the CAMP in Iberia. The intrusion of magmatic bodies was mostly controlled by the crustal tectonic fabric inherited from the Paleozoic Variscan orogeny, which was re-worked during the Mesozoic rifting and the Cenozoic Alpine collision. Plain Language Summary The opening and closing of oceans and welding of supercontinents can be accompanied by large areas affected by magmatism unrelated to oceanic drifting implying independent geodynamic causes. We investigate the distribution of two magmatic events: the similar to 200 million years (Ma) Central Atlantic Magmatic Province (CAMP) and the West Iberia Late Cretaceous Alkaline Province (WILCAP) formed between 94 and 72 Ma ago. CAMP is the largest Large Igneous Province on Earth (spanning from Central Brazil to northern France), however its volcanic activity did not last more than 1 Ma. WILCAP has a much smaller extent but lasted more than 20 Ma. CAMP is represented by similar to 400 m thick lava flows and their deep sources were only first reported in 2021. WILCAP is known for km-scale massifs of peculiar magmatic rocks (Sintra, Sines, Monchique) and other volcanic and intrusive rocks occurring onshore West Portugal. We present new marine magnetic maps for similar to 4,400 km(2) that reveal complex magnetic anomalies, unraveling the cause of the Cabo Raso magnetic anomaly near Lisbon known since the 15th century by Portuguese navigators for deflecting the ship compasses; discovering the Covo buried intrusion, so far the largest off West Iberia; discovering a new deep source of the CAMP volcanism.