The Rift and Continent-Ocean Transition Structure Under the Tagus Abyssal Plain West of the Iberia

22 pages, 9 figures, supporting information https://doi.org/10.1029/2021JB022629.-- Data Availability Statement: Seismic and gravity data were collected by Spanish R/V Sarmiento de Gamboa in 2018. High-resolution images of the data used in this article are available in Figshare public database (https://figshare.com/articles/figure/MCS-seismic-line-interpreted_pdf/14865480 and https://figshare.com/articles/figure/OBS_H-seismic-record-sections_pdf/14865483). The bathymetric grid is freely available as a.xyz file from the website of the EMODnet (https://www.emodnet-bathymetry.eu/) and Generic Mapping Tools (Wessel & Smith, 1995) was used in the preparation of this manuscript.-- This is a contribution of the Barcelona Center for Subsurface Imaging that is a Grup de Recerca 2017 SGR 1662 de la Generalitat de CatalunyaThe West Iberia margin is the focus of intense research since the 1980s, with some of the most exemplary geophysical cross-sections and drilling expeditions. Those data sets have been used to create conceptual models of rifting used as a template to interpret margins worldwide. We present two collocated ∼350 km long lines of multi-channel seismic (MCS) streamer data and wide-angle seismic (WAS) data collected across the Tagus Abyssal Plain (TAP). We use travel-times of first arrivals identified at WAS and reflected seismic phases identified at both WAS and MCS records to jointly invert for the P wave velocity (Vp) distribution and the geometry of a sediment unconformity, the top of the basement, and the Moho boundary. The Vp model shows that the TAP basement is more complex than previously inferred, presenting abrupt boundaries between five domains. Domain I under the foot of the slope and Domain III under the abyssal plain display Vp values and gradients of thin continental crust. In between, Domain II displays a steep Vp gradient and high Vp values at shallow depth that support that basement is made of exhumed partly serpentinized mantle. Domain IV and Domain V, further oceanward, have oceanic crust Vp structure. The new results support an unanticipated complex rift history during the initial separation of Iberia and America. We propose a geodynamic scenario characterized by two phases of extension separated by a jump of the locus of extension, caused by the northward propagation of the oceanic spreading center during the J-anomaly formation, which terminated continental riftingThe Spanish Ministry of Science, Innovation and Universities funded the FRAME project (CTM2015-71766-R) and I. Merino Ph.D. (BES-2016-077786). M. Prada is supported by the Beatriu de Pinós postdoctoral programme of the Catalonia Government (2017BP00170). [...] With the institutional support of the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S)Peer reviewe