MARIBNO amphibious project: Structure of the northwestern Iberian margin and role of the inherited tectonics in the Alpine extension and inversion

The northwestern margin of the Iberian Peninsula (western Bay of Biscay) is a unique place that gathers several outstanding geological features in a relatively reduced area. Here, a former hyperextended continental margin developed in proximity to a triple point, underwent a subsequent partial tectonic inversion yielding the present Cantabrian margin. For all these reasons, the northwest area of ​​Iberia can be considered as a natural laboratory for the study of the role of tectonic inheritance in the evolution of the extensional continental margins and their subsequent inversion. However, and largely due to the lack of interest from exploration companies, the northwestern margin of Iberia presented a great deficit of geophysical and geological information. Both scientific interest and the lack of information provided the main reasons for the MARIBNO amphibious project (2019-2022). This project is being carried out by a multidisciplinary geoscientific team leaded by the Complutense University of Madrid with the acquisition of offshore and onshore data. The main objectives are focused on the study of the crustal structure, the tectonic control by the structure prior to the alpine stages and the mapping and characterization of the crustal domains, combining geological and geophysical criteria.

A one month-long geophysical cruise was carried out aboard the BO Sarmiento de Gamboa (Spanish Research Council, CSIC) in September-October of 2021. Data acquisition was divided in two cruise legs: The WAS Leg consisted in the acquisition wide-angle seismic data (WAS) along 3 transects with simultaneous offshore-onshore recording in 3 component short-period instruments: Transect WAS-1 (∼320 km) recorded in 14 OBS and 11 land seismometers, Transect WAS-2 (∼260 km) recorded in 12 OBS and 10 land seismometers and Transect WAS-3 (∼255 km) recorded in 9 OBS and 12 land seismometers. The seismic source consisted in an airgun array with 4660 ci and 90 seconds of shot interval. The MCS leg consisted in the acquisition of 2D multichannel seismic reflection data (MCS) along 14 transects (∼1500 km) recorded on a digital streamer with a 12.5 m channel-interval. Several streamer configurations were deployed with 480, 240 and 168 channels and the seismic source consisted in an airgun array with 1960 ci. During both legs, continuous marine acquisition of multibeam bathymetry, gravity, geomagnetics and ultra-high resolution seismic data also were carried out. MARIBNO project is still underway, and the data are being processed and interpreted. Acquired information will be complemented and combined with the additional acquisition of onshore gravity and magnetic data and the information from several geological field mapping studies on seismic transects throughout the Cantabrian Mountains. Here we show some preliminary results and the current development of the MARIBNO amphibious project.