American Geophysical Union Meeting (AGU23), 11-15 December 2023, San Francisco, The J magnetic anomaly is a >1000 km long seafloor-spreading lineation ~125-120 Ma in the northern sector of the Central Atlantic crust in both the African and conjugate American plates. There, the J magnetic anomaly integrates the M3-M0 anomalies of the Cretaceous M-series, but displays anomalously high amplitude values of 200-400 nT, i.e. up to 20 times larger than similar age anomalies.

More intriguing is that the J magnetic anomaly appears to extend into the West Iberia rifted continental margin, whereas there is no clear similarly high-amplitude linear magnetic anomaly in the conjugate Canadian margin.

The origin of the J-magnetic anomaly in the central Atlantic is undisputedly oceanic but the cause for its high magnetic amplitude has not yet been explained.
The origin of the J-magnetic anomaly in the West Iberia margin is highly disputed, namely for its its age and origin (e.g. synrift magmatism or seafloor spreading), and even whether it represents the extension to the north of the oceanic J-anomaly or is an unrelated structure (with different age and origin).
We present a new geophysical dataset collected in 2022 across the J anomaly in the African plate that allows discussing the nature of the anomaly where it was first described and defined. Then, we compare the results with a new interpretation of the also called J magnetic anomaly off West Iberia.
We will provide new information and modelling regarding the origin of the high amplitude and discuss the similarities and differences between the anomalies in the African and Iberia plates to evaluate the possibility of a common origin of the magnetic lineations, This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL. Support from FCT (PTDC/CTA-GEF/1666/2020), Spanish Ministry of Science and Innovation (CTM2015-71766-R, PID2019-109559RB-I00) and Spanish Research Agency (CEX2019-000928-S) is also acknowledged, Peer reviewed

European Geosciences Union General Assembly (EGU23), 24-28 April 2023, Vienna, Austria.-- 1 page, The conceptual models of magma-poor rifted margins are greatly influenced by the continent-to-ocean transition structure of the archetypal magma-poor West Iberia Margin. Some previous works with West Iberia magnetic data have been used to constrain the structure and interpret the transition from the exhumed mantle domain to the oceanic crust formed at a spreading center. However, it is found that the resolution uncertainty of the geophysical data was generally overlooked, leading to over-detailed interpretations. In this work we use synthetic magnetic modelling to show that magnetic data acquired at sea-level cannot resolve sub-horizontal lithological layering in deep-water continental margins. Then, we present a new magnetic model guided by a refined velocity model of the wide-angle seismic IAM-9 profile in the Iberia Abyssal Plain. This new model supports that the J-anomaly is caused by a ~6 km thick oceanic crustal structure with locally increased magnetization compared to regular oceanic crust. This J-anomaly crust abuts the exhumed mantle across a nearly vertical boundary, and is the oldest accreted oceanic crust. These results support that mantle exhumation was abruptly terminated by the accretion of oceanic crust. Mantle melting creating oceanic crust was probably not driven by gradual lithospheric thinning and asthenospheric upwelling, but may be the result of seafloor spreading center propagation cutting across the lithosphere and creating the abrupt structure, This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL. Support from FCT (PTDC/CTA-GEF/1666/2020), Spanish Ministry of Science and Innovation (CTM2015-71766-R, PID2019-109559RB-I00) and Spanish Research Agency (CEX2019-000928-S) is also acknowledged, Peer reviewed