Submarine basalt xenoliths confirm the occurrence of post-rift volcanism in the Southern Santos Basin, SW Atlantic

We report here the finding and analysis of xenoliths of altered basalt clasts dredged from the top of two exhumed diapirs in the southern Santos Basin (SW Atlantic). The diapirs crossed the stratigraphic column from the Aptian and outcropped on the seafloor. Complemented by seismic data, these findings provide the first direct evidence of an Early Campanian post-rift magmatic event in the southern Santos Basin (SW Atlantic). One 82 Ma Ar-Ar age of these xenoliths indicates that the volcanism developed coeval with the intrusion of the Serra do Mar Alkaline Province rocks on land. The tholeiitic composition of the xenoliths excludes a genetic correlation with the alkaline province. Seismic reflection data indicate the possible source of the xenoliths from a 40-km-wide cluster of volcanic centers and sills located above the Aptian salt deposits (similar to 115 Ma), between the top-Turonian (90 Ma) and top-Campanian (72 Ma) interval. We suggest that salt diapirism peented the overlaying volcanic units and carried fragments upwards through the entire stratigraphic column to the ocean floor. Our findings stress that salt diapirism is an important mechanism for conveying unreachable subsurface fragments to the surface, particularly the ocean floor. With the expanding knowledge of the seascape worldwide, enhanced exploration of salt diapirism and its xenolith products has the potential of opening new windows to unknown parts of geologic history.

Automated summary

This study reports the discovery and analysis of xenoliths of altered basalt clasts found in two exhumed diapirs in the southern Santos Basin in the SW Atlantic. These xenoliths provide direct evidence of an Early Campanian post-rift magmatic event in the area and are possibly sourced from a cluster of volcanic centers and sills above the Aptian salt deposits. The findings highlight the importance of salt diapirism in transporting subsurface fragments to the ocean floor, and suggest that further exploration of salt diapirism could reveal unknown aspects of geological history.