The Catalan magnetic anomaly: Its significance for the crustal structure of the Gulf of Lion passive margin and relationship to the Catalan transfer zone

Abstract

Abstract The western part of the Gulf of Lion (GoL) passive margin, at the foot of the Pyrenees mountain chain, hosts the Catalan magnetic anomaly (CMA), a significant NW-SE-trending linear magnetic anomaly 50 km long with no associated gravimetric signal. The CMA is located on the continental slope near the NW-SE-trending Catalan transfer zone (CTZ), and it extends from the shelfbreak to the abyssal plain across thinned to hyper-thinned continental domain. This study interprets an updated geophysical dataset to better understand the Pyrenees–GoL transition and proposes a new interpretation of the CMA's source. Gravimetric and magnetic modelling of the lithosphere along two perpendicular cross-sections indicates that the CMA is generated by a magnetic body (80 × 20 × 12 km), called here the Catalan body, within the thinned continental domain. We interpret it as a mass of mafic material underplating and intruding the continental crust along a crustal fault belonging to the CTZ system. From the new map of Moho depths, a wide NW-SE-trending zone is highlighted on the western extremity of the GoL margin at the foot of the eastern Pyrenees Chain. It is characterized by (i) a heterogeneous crustal structure and mantle rise underneath the Tertiary Catalan sedimentary basin in the continental shelf area, (ii) a necking zone in a more proximal location compared to the eastern GoL margin, and (iii) the presence of magmatism (Catalan body) under and in the thinned continental crust, in the necking zone domain. These characteristics may be induced by the transtensional motion along the CTZ during the Tertiary opening of the Liguro-Provencal Basin, contemporary with the extension of the GoL margin. However, the role of inherited structures from the Hercynian orogeny, Mesozoic rifting and Pyrenean orogeny cannot be excluded when explaining the crustal heterogeneity, transfer zones and Moho morphology in this region.