Paleomagnetism of the Central Atlantic Magmatic Province in the Algarve basin, Portugal: First insights

- The remanent magnetization of the CAMP lavas is primary.
- Paleomagnetic poles of Group A are comparable to the 200-Ma Messejana pole.
- Group B shows distinct directions suggesting clockwise vertical-axis rotation (~ 30º).
- Block rotation may have been produced by a strike-slip shear zone acting during the Cenozoic.

We present new rock magnetic and paleomagnetic data of the Central Atlantic Magmatic Province (CAMP) lavas cropping out in the Algarve basin (southern Portugal). Our results show that the magnetic mineralogy of the selected samples is primary and dominated by an assemblage of single-domain (SD) to multi-domain (MD) Ti-poor titanomagnetites. All samples carry a characteristic remanent magnetization of normal (positive) magnetic polarity, similarly to other circum-Atlantic CAMP lava sequences. Except for the sites located in the central part of the Algarve basin, site-based mean directions (5 sites, Group A) are comparable to the giant Messejana dyke's directions, suggesting that both lava flows and dyke were emplaced during the same geological interval (~ 200 Ma). However, sites located in the central part of the basin (4 sites; Group B), just east of the São Marcos-Quarteira fault zone, show a systematic discrepancy in the declination values, which is indicative of a significant vertical-axis rotation that we estimated to be ~ 30° clockwise. We suggest that the observed clockwise vertical-axis rotation was produced by a Riedel dextral shear zone of the São Marcos-Quarteira faults acting during the N-S compression that affected the Southern Portuguese margin in the Cenozoic. Our results provide important insights to unravel the complex history of the Algarve basin since the Mesozoic.