Magmatic cycles in Santos Basin (S.E. Brazil): Tectonic control in the temporal-spatial distribution and geophysical signature

Abstract

The Santos Basin, in the offshore southeastern Brazilian margin, evolved from a continental rift system to a passive divergent margin during the Cretaceous as a onsequence of the Gondwana breakup and the formation of the proto-Atlantic Ocean. The basin exhibits several cycles of magmatism from Valanginian to Eocene times, with a regionalized distribution of igneous rocks. Using seismic, gravity, magnetic, and wellbore data, the magmatic cycles were investigated and connected with the basin's tectonic activity. Our study includes a regional analysis of the various magmatic cycles, with a focus on identifying the temporal variations and spatial differences observed in the basin's many tectonic compartments. The first magmatic cycle, named rift-onset, is observed in both coastal and offshore regions and includes magmatic rocks from ca.135 to ca. 132/130 Ma. Onshore, the rift-onset magmatic rocks are observed in the coastal dike swarm province and in the coastal alkaline province. Offshore, the riftonset is observed as a prolongation of the coastal dike swarms into the proximal basin and as flood basalts in the distal basin. The second cycle includes the synrift (ca.132-130 to 123 Ma) and postrift (ca.123 to 113-112 Ma) magmatic rocks. The separation of intrusive synrift and postrift rocks is challenging in the onshore fieldwork and in the seismic analyses offshore, which is aggravated by the basin's scarcity of geochronological dating. Therefore, these two events have been treated together when the separation is not clear. The third cycle comprises the drift (or post breakup) magmatic rocks, spanning from the Lower Cretaceous to the Tertiary (from ca. 110 to ca. 40 Ma), and is well documented in coastal and offshore domains. Drift magmatism seems to be controlled by tectonics, since magmatic bodies tend to concentrate along lines of crustal discontinuities. Magmatic cycles (rift-onset, syn/postrift, and drift) also display spatial differences, exhibiting variation in the magmatic volume and in the morphology of igneous rocks from the southern to the central/northern Santos Basin. The study of magmatism in the, Santos Basin offers an excellent opportunity to investigate the processes that occurredduring the evolution of a volcanic rifted margin.